After a Decade of Radio Silence, a Mysterious Star Is Showing Signs of Waking Up


After more than a decade of patiently waiting and watching, astronomers have seen signs that one of the rarest stars known to science is waking up from its slumber.

It’s called XTE J1810–197, and it’s part of an exclusive club of weird stars – it’s one of just four highly magnetic magnetars that have been found to emit radio waves.

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At least it did, until a decade ago when those radio waves went quiet. Now it’s stirring again, and astronomers have their telescopes at the ready to record.

That might not sound that exciting, but magnetars themselves are incredibly weird. They’re essentially ‘dead’ stars that, for reasons we don’t fully understand, have insanely powerful magnetic fields.

To put it into perspective these incredibly dense, collapsed stars can generate magnetic fields that are around 1 quadrillion times more powerful than Earth’s. So, yeah, they’re odd.

We currently know of 23 magnetars, but XTE J1810–197 is something else entirely. While magnetars all blast out high energy stuff, XTE J1810–197 and only three other stars we’ve found pulse out radio waves.

And then, in late 2008, its radio waves suddenly went quiet, and stayed that way.

Until now.

Since December 8 last year, researchers from the University of Manchester and Max-Planck-Institut fur Radioastronomie have been monitoring a fresh stream of radio emissions from the most unusual cosmic object.

Interestingly, the profile of this new rhythm of radio waves shows some pretty big differences since they were first noticed all those years ago.

“The pulse variations seen so far from the source have been significantly less dramatic, on timescales from hours to months, than seen in 2006,” the research team report.

Among them are tiny ripples of activity on a millisecond scale that might be caused by tiny shivers in the star’s crust.

The thing is we still don’t know a lot about magnetars. They seem to form in the same way as your average neutron star, starting with the collapsing core of a massive, dying star squeezing atoms so their nuclei are pressed butt-to-cheek.

At some point the compact body starts to generate magnetic fields in the order of around 10^15 gauss. By comparison, a typical fridge magnet is around 50 gauss, which is still 100 times stronger than our planet’s magnetic field at the surface.

What causes such powerful magnetism is a mystery, with most theories suggesting it could all start with the neutron star spinning at hundreds to thousands of times per second and turning into a pulsar.

Think of a bunch of suns crammed into a space the size of a small city whipping around with the ferocity of a helicopter’s blades and you can begin to imagine these monsters.

If that’s not intense enough, since their prediction in the late 80s, magnetars have become associated with strange, irregular bursts of gamma and X-ray radiation that repeat in some parts of the sky.

The going explanation for these massive outbursts of powerful radiation is adjustments in the star’s neutron-packed crust – the magnetar equivalent of an earthquake – tug its magnetic field into new alignments.

The weird thing about XTE J1810–197 is a year after it briefly shone in X-rays back in 2003, astronomers noticed it was sighing in pulses of far gentler radio waves. Initial observations noticed it was spitting out low energy electromagnetic radiation once a turn, about every five and a half seconds.

It was the first of just a handful of radio-emitting magnetars that have since been discovered.

This exclusive class of star blurs the lines between these magnetic monsters and garden variety pulsars, their own weaker magnetic fields channelling beams of radiation that glow in radio waves that sweep across the cosmos as they spin.

Maybe all magnetars produce radio waves in similar ways and we only see them in a few? Perhaps there’s something special about XTE J1810–197 and the other three radio-emitting magnetars?

Going on this new study, it’s possible that tremors in the star’s crust of packed neutrons not only realign its powerful magnetic field, but directly contribute to a range of electromagnetic frequencies that include radio waves.

The research is currently available on the pre-review site, arxiv.org, so it’s set to generate some discussion.

Another teams of astronomers recently used NASA’s Deep Space Network to check out XTE J1810–197 and two of its radio magnetar cousins. They also happened to notice some odd variations in the radio wave emissions.

Future observations might help whittle away speculations on what’s behind these pulses, and why they come and go as they do.

Now that one of the beasts is awake again, it might yet have more to say on the matter.

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Saturn is officially losing its rings – and they’re disappearing much faster than scientists had anticipated


  • Saturn is losing its rings.
  • New data from NASA’s former Cassini spacecraft has revealed that the rings will be gone 200 million years sooner than previously estimated.
  • We explain what’s going on with Saturn’s rings and why they’re disappearing at a faster rate than previously thought.

If you were to pick Saturn out of a lineup you’d probably recognize it by its iconic rings. They’re the biggest, brightest rings in our solar system. Extending over 280,000 km from the planet; wide enough to fit 6 Earths in a row. But Saturn won’t always look this way. Because its rings are disappearing.

That’s right, Saturn is losing its rings! And fast. Much faster, even, than scientists had first thought. Right now, it’s raining 10,000 kilograms of ring rain on Saturn per second. Fast enough to fill an Olympic-sized pool in half an hour.

This rain is actually the disintegrated remains of Saturn’s rings. Saturn’s rings are mostly made up of chunks of ice and rock. Which are under constant bombardment: Some by UV radiation from the Sun and others by tiny meteoroids.

When these collisions take place, the icy particles vaporize, forming charged water molecules that interact with Saturn’s magnetic field; ultimately, falling toward Saturn, where they burn up in the atmosphere.

Now, we’ve known about ring rain since the 1980s when NASA’s Voyager mission first noticed mysterious, dark bands that turned out to be ring rain caught in Saturn’s magnetic fields. Back then, researchers estimated the rings would totally drain in 300 million years. But observations by NASA’s former Cassini spacecraft give a darker prognosis. Before its death dive into Saturn in 2017, Cassini managed to get a better look at the amount of ring-dust raining on Saturn’s equator.

And discovered that it was raining heavier than previously thought. With these clearer observations, scientists calculated the rings had only 100 million years left to live. Now, it’s tough to imagine a ringless Saturn.

But for much of its existence, the planet was as naked as Earth. While Saturn first formed around 4.5 BILLION years ago, studies suggest the rings are only 100- 200 million years old, tops. That’s younger than some dinosaurs.

So when you think about it, we’re pretty lucky we happened to be around to see those magnificent rings. Really lucky, in fact. Because efforts to study those rings have led us to other discoveries.

For example, as Cassini explored Saturn’s moon Enceladus, it uncovered a trail of ice and gas leading back to Saturn’s E ring. Enceladus is the whitest, most reflective moon in our solar system.

And by studying the ring more closely, scientists now know why. Turns out, the moon is constantly gushing out gas and dust.

Some of it ends up in space and in the E ring while the rest snows back onto the moon’s surface, creating a blinding white frost.

So, who knows what other discoveries might be hiding within the rings? At the very least, it’s clear we’d better keep looking while we still can.

9 of the Most Important Telescopes in the Universe of Astronomy


These telescopes have changed the course of history, reshaping our understanding of the universe.

 

The first optical telescope was created a little over 400 years ago. Though it is safe to assume that the technology found in telescopes has vastly improved, the mission is still the same. Astronomers and researchers alike use telescopes as their main tool to explore the universe, to peer into the great beyond, and to gain further insight into humanity’s place within it.

Coined by the Greek mathematician Giovanni Demisiani telescopes are optical instruments that make distant objects appear magnified by using an arrangement of lenses or curved mirrors and lenses, or various devices used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation.

Across the planet, telescopes have been used to view distant stars and galaxies, as well as countless other celestial objects. Who knows, maybe a few aliens might have popped up on a few lenses.

Currently, there are seven classifications of telescopes that astronomers use, most of them is a big step from what you may have had laying in your bedroom as a kid. Each telescope uses a different method to scan the sky. There are x-ray telescopes, ultraviolet telescopes, optical telescopes, infrared telescopes, submillimeter telescopes, fresnel imagers, and finally x-ray optics.

Here is a little refresher crash course on everything you need to know about telescopes.

Now that you have got the basics down it is time to venture off and examine some of the most important telescopes in astronomy.

Galileo’s Telescope

Why not start where it all began? Though Galileo Galilei was not the inventor of the telescope or even the first person to point a spyglass up into the sky, he was one of the first astronomers to extrapolate what he saw in the night sky drawing conclusions about the universe that would forever change the way people viewed the night sky

His work would eventually earn him the title “ The Father of Modern Science”. Using his telescope, Galileo was busy observing the moon, discovering four of Jupiter’s moons, watching supernovas, and even verified the phases of Venus.

The Fermi Gamma-ray Telescope

As its name implies, The Fermi Gamma-ray Telescope uses gamma rays. A form of light, gamma rays are some of the most powerful forms of energy in the universe. Gamma-ray bursts tend to be created during the violent collision of stars or even in celestial events like black holes.

Hubble Space Telescope

9 of the Most Important Telescopes in the Universe of Astronomy
Source: NASA

Now, let’s move on to something that is more of a household name, the Hubble Telescope. Being in orbit for almost 30 years, the telescope takes its name from the famous American Astronomer Edwin Hubble. Even if you have never heard about this telescope, you have for sure heard of some the Hubble’s tremendous accomplishments.

9 of the Most Important Telescopes in the Universe of Astronomy
Source: NASA

The Hubble Telescope has helped astronomers accurately estimate the age of the universe, gain further understanding of the planets in our solar system while taking shots at other exoplanets, and even snapping shots of other infant galaxies.

The MeerKAT Radio Telescope

9 of the Most Important Telescopes in the Universe of Astronomy
Source: SARAO

The force is strong with this one. Based in South Africa, the MeerKAT radio telescope has one of the more unique functions on this list. Comprising of 64 radio dishes, this telescope station will help astronomers gain further insight into dark matter and the gradual evolution of galaxies.

9 of the Most Important Telescopes in the Universe of Astronomy
Source: NASA

Already spotting more than 1,300 new galaxies, the MeerKAT is the largest and most sensitive radio telescope in the southern hemisphere.

Gemini Observatory

The Gemini Observatory is one of the more unique tools used by astronomers. Owned by seven different countries across the globe, the observatory is comprised of two identical 8.1-meter telescopes with one on Hawaii’s Mauna Kea and another on central Chile’s Cerro Pachón; oceans apart.

9 of the Most Important Telescopes in the Universe of Astronomy
Source: The Gemini Observatory 

Gemini’s unique and advanced infrared capabilities, as well as its optical tech, allow it to probe into areas of the universe that would be otherwise impossible to see. The Gemini Observatory has observed everything from the birth of a supernova to a potentially habitable Earth-like planet.

The Spitzer Space Telescope

The Spitzer Space Telescope was launched in 2003 with the specific purpose of studying the early universe in infrared light. As one of the first telescopes to see light from a planet outside the solar system, Spitzer has made some impressive discoveries, finding fresh new comets, stars, exoplanets, and distant galaxies.

 The Kepler Telescope

9 of the Most Important Telescopes in the Universe of Astronomy
Source: NASA

The planet hunter, the Kepler Telescope was created to scour the universe for any potential alien life and planets. Now officially in retirement, the telescope has discovered well over 2,600 planets outside our solar system during its nine-year career, making it one of the most successful telescopes ever.

9 of the Most Important Telescopes in the Universe of Astronomy
Source: NASA

The Atacama Large Millimeter/submillimeter Array

9 of the Most Important Telescopes in the Universe of Astronomy
Source: NASA

Spread across 10 miles and featuring 66 radio antennas 16,000 feet up in the Chilean Andes, these radio telescopes were once considered some of the most powerful and advanced on earth. Their discoveries laid the foundation for astronomer’s understanding of exoplanets.

 The W.M. Keck Observatory

9 of the Most Important Telescopes in the Universe of Astronomy
Source: NASA

Located on the top of Mauna Kea, a dormant volcano in Hawaii, The W.M. Keck Observatory has been operating since 1993. Featuring two massive 33 feet in diameter telescopes, the station offers the largest optical and infrared telescopes in the world.

The massive telescopes have proven to be fruitful churning out dozens of amazing discoveries. Each telescope has peered in the center of the Milky Way Galaxy, provided scientists more information on the Universe’s accelerated growth, and provided the first pictures of an exoplanet system,  just to name a few.

Scientists Debate Signatures of Alien Life


Searching for signs of life on faraway planets, astrobiologists must decide which telltale biosignature gases to target.

 

Huddled in a coffee shop one drizzly Seattle morning six years ago, the astrobiologist Shawn Domagal-Goldman stared blankly at his laptop screen, paralyzed. He had been running a simulation of an evolving planet, when suddenly oxygen started accumulating in the virtual planet’s atmosphere. Up the concentration ticked, from 0 to 5 to 10 percent.

“Is something wrong?” his wife asked.

“Yeah.”

The rise of oxygen was bad news for the search for extraterrestrial life.

After millennia of wondering whether we’re alone in the universe — one of “mankind’s most profound and probably earliest questions beyond, ‘What are you going to have for dinner?’” as the NASA astrobiologist Lynn Rothschild put it — the hunt for life on other planets is now ramping up in a serious way. Thousands of exoplanets, or planets orbiting stars other than the sun, have been discovered in the past decade. Among them are potential super-Earths, sub-Neptunes, hot Jupiters and worlds such as Kepler-452b, a possibly rocky, watery “Earth cousin” located 1,400 light-years from here. Starting in 2018 with the expected launch of NASA’s James Webb Space Telescope, astronomers will be able to peer across the light-years and scope out the atmospheres of the most promising exoplanets. They will look for the presence of “biosignature gases,” vapors that could only be produced by alien life.

They’ll do this by observing the thin ring of starlight around an exoplanet while it is positioned in front of its parent star. Gases in the exoplanet’s atmosphere will absorb certain frequencies of the starlight, leaving telltale dips in the spectrum.

Filming by Tom Hurwitz and Richard Fleming. Editing and motion graphics by Ryan Griffin. Other graphics and images from NASA, the European Southern Observatory and Creative Commons. Music by Podington Bear.

In Theory Video: David Kaplan explores the best ways to search for alien life on distant planets.

As Domagal-Goldman, then a researcher at the University of Washington’s Virtual Planetary Laboratory (VPL), well knew, the gold standard in biosignature gases is oxygen. Not only is oxygen produced in abundance by Earth’s flora — and thus, possibly, other planets’ — but 50 years of conventional wisdom held that it could not be produced at detectable levels by geology or photochemistry alone, making it a forgery-proof signature of life. Oxygen filled the sky on Domagal-Goldman’s simulated world, however, not as a result of biological activity there, but because extreme solar radiation was stripping oxygen atoms off carbon dioxide molecules in the air faster than they could recombine. This biosignature could be forged after all.

The search for biosignature gases around faraway exoplanets “is an inherently messy problem,” said Victoria Meadows, an Australian powerhouse who heads VPL. In the years since Domagal-Goldman’s discovery, Meadows has charged her team of 75 with identifying the major “oxygen false positives” that can arise on exoplanets, as well as ways to distinguish these false alarms from true oxygenic signs of biological activity. Meadows still thinks oxygen is the best biosignature gas. But, she said, “if I’m going to look for this, I want to make sure that when I see it, I know what I’m seeing.”

Meanwhile, Sara Seager, a dogged hunter of “twin Earths” at the Massachusetts Institute of Technology who is widely credited with inventing the spectral technique for analyzing exoplanet atmospheres, is pushing research on biosignature gases in a different direction. Seager acknowledges that oxygen is promising, but she urges the astrobiology community to be less terra-centric in its view of how alien life might operate — to think beyond Earth’s geochemistry and the particular air we breathe. “My view is that we do not want to leave a single stone unturned; we need to consider everything,” she said.

As future telescopes widen the survey of Earth-like worlds, it’s only a matter of time before a potential biosignature gas is detected in a faraway sky. It will look like the discovery of all time: evidence that we are not alone. But how will we know for sure?

Scientists must quickly hone their models and address the caveats if they are to select the best exoplanets to target with the James Webb telescope. Because of the hundreds of hours it will take to examine the spectrum for each planetary atmosphere and the many competing demands on its time, the telescope will likely only observe between one and three earthlike worlds in the habitable “Goldilocks” zones of nearby stars. In choosing from a growing list of known exoplanets, the scientists want to avoid planetary circumstances in which oxygen false positives arise. “We’re looking at maybe putting our eggs, if not all in one basket, at least in only a couple of baskets,” Meadows said, “so it’s important to try and figure out what we should be looking for there. And in particular, how we might get fooled.”

Breath of Life

Oxygen has been regarded as the gold standard since the chemist James Lovelock first contemplated biosignature gases in 1965, while working for NASA on methods of detecting life on Mars. As Frank Drake and other pioneers of astrobiology sought to detect radio signals coming from distant alien civilizations — an ongoing effort called the search for extraterrestrial intelligence (SETI) — Lovelock reasoned that the presence of life on other planets could be deduced by looking for incompatible gases in their atmospheres. If two gases that react with each other can both be detected, then some lively biochemistry must be continually replenishing the planet’s atmospheric supplies.

In Earth’s case, though it readily reacts with hydrocarbons and minerals in the air and ground to produce water and carbon dioxide, diatomic oxygen (O2) comprises a steady 21 percent of the atmosphere. Oxygen persists because it is poured into the sky by Earth’s photosynthesizers — plants, algae and cyanobacteria. They enlist sunlight to strip hydrogen atoms off water molecules, building carbohydrates and releasing the oxygen byproduct as waste. If photosynthesis ceased, the existing oxygen in the sky would react with elements in the crust and drop to trace levels in 10 million years. Eventually, Earth would resemble Mars, with its carbon dioxide-filled air and rusty, oxidized surface — evidence, Lovelock argued, that the Red Planet does not currently harbor life.

But while oxygen is a trademark of life on Earth, why should that be true elsewhere? Meadows argues that photosynthesis offers such a clear evolutionary advantage that it is likely to become widespread in any biosphere. Photosynthesis puts the biggest source of energy on any planet, its sun, to work on the most commonplace of planetary raw materials: water and carbon dioxide. “If you want to have the uber-metabolism you will try and evolve something that will allow you to use sunlight, because that’s where it’s at,” Meadows said.

Diatomic oxygen also boasts strong absorption bands in the visible and near-infrared — the exact sensitivity range of both the $8 billion James Webb telescope and the Wide Field Infrared Survey Telescope (WFIRST), a mission planned for the 2020s. With so many imminent hopes riding on oxygen, Meadows is determined to know “where the gotchas are likely to be.” So far, her team has identified three major nonbiological mechanisms that can flood an atmosphere with oxygen, producing false positives for life. On planets that formed around small, young M-dwarf stars, for instance, intense ultraviolet sunlight can in certain cases boil down the planet’s oceans, creating an atmosphere thick with water vapor. At high altitudes, as VPL scientists reported in the journal Astrobiology last year, intense UV radiation splinters off the lightweight hydrogen atoms. These atoms then escape to space, leaving behind a veil of oxygen thousands of times denser than Earth’s atmosphere.

Because the smallness of M-dwarf stars makes it easier to detect much smaller, rocky planets passing in front of them, they are the intended targets for NASA’s Transiting Exoplanet Survey Satellite (TESS), a planet-finding mission scheduled to launch next year. The earthlike planets that will be studied by the James Webb telescope will be selected from among TESS’s finds. With these candidates on the way, astrobiologists must learn how to distinguish between alien photosynthesizers and runaway ocean boiling. In work that is now being prepared for publication, Meadows and her team show that a spectral absorption band from tetraoxygen (O4) loosely forms when O2 molecules collide. The denser the O2 in an atmosphere, the more molecular collisions occur and the stronger the tetraoxygen signal becomes. “We can look for the [O4] to give us the telltale sign that we’re not just looking at a 1-bar atmosphere with 20 percent oxygen” — an earthlike atmosphere suggestive of photosynthesis — Meadows explained, “we’re looking at something that just has massive amounts of oxygen in it.”

A strong carbon monoxide signal will identify the false positive that Domagal-Goldman first encountered that drizzly morning in 2010. Now a research scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md., he says he isn’t worried about oxygen’s long-term prospects as a reliable biosignature gas. Oxygen false positives only happen in rare cases, he said, “and the planet that has those certain cases is also going to have observational properties that we should be able to detect, as long as we think about it in advance, which is what we’re doing right now.”

He and other astrobiologists are also mindful, though, of oxygen false negatives — planets that harbor life but have no detectable oxygen in their atmospheres. Both the false positives and false negatives have helped convince Sara Seager of the need to think beyond oxygen and explore quirkier biosignatures.

Encyclopedia of Gases

If the diverse exoplanet discoveries of the past decade have taught us anything, it’s that planetary sizes, compositions and chemistries vary dramatically. By treating oxygen as the be-all, end-all biosignature gas, Seager argues, we might miss something. And with a personal dream of discovering signs of alien life, the 44-year-old can’t abide by that.

Even on Earth, Seager points out, photosynthesizers were pumping out oxygen for hundreds of millions of years before the process overwhelmed Earth’s oxygen sinks and oxygen started accumulating in the sky, 2.4 billion years ago. Until about 600 million years ago, judged from a distance by its oxygen levels alone, Earth might have appeared lifeless.

Meadows and her collaborators have studied some alternatives to oxygenic photosynthesis. But Seager, along with William Bains and Janusz Petkowski, are championing what they call the “all-molecules” approach. They’re compiling an exhaustive database of molecules — 14,000 so far — that could plausibly exist in gas form. On Earth, many of these molecules are emitted in trace amounts by exotic creatures huddled in ocean vents and other extreme milieus; they don’t accumulate in the atmosphere. The gases might accrue in other planetary contexts, however. On methane-rich planets, as the researchers argued in 2014, photosynthesizers might harvest carbon from methane (CH4) rather than CO2 and spew hydrogen rather than oxygen, leading to an abundance of ammonia. “The ultimate, long-term goal is [to] look at another world and make some informed guesses as to what life might produce on that world,” said Bains, who splits his time between MIT and Rufus Scientific in the United Kingdom.

Domagal-Goldman agrees that thinking both deeply about oxygen and broadly about all the other biochemical possibilities is important. “Because all these surprises have happened in our detections of the masses and radii and orbital properties of these other worlds,” he said, “[astronomers] are going to keep pushing on the people like me who come from an earth sciences background, saying, ‘Let’s think further outside the box.’ That is a healthy and necessary pressure.”

Meadows, however, questions the practicality of the all-molecules approach. In a 3,000-word email critiquing Seager’s ideas, she wrote, “After you build this exhaustive database, how do you identify those molecules that are most likely to be produced by life? And how do you identify their false positives?” She concluded: “You will still have to be guided by life on Earth, and our understanding of planetary environments and how life interacts with those environments.”

In contemplating what life might be like, it’s exasperatingly difficult to escape the only data point we have — for now.

Uncertain Odds

At a 2013 symposium, Seager presented a revised version of the Drake equation, Frank Drake’s famous 1961 formula for gauging the odds that SETI would succeed. Whereas the Drake equation multiplied a string of mostly unknown factors to estimate the number of radio-broadcasting civilizations in the galaxy, Seager’s equation estimates the number of planets with detectable biosignature gases. With the modern capacity to look for any life regardless of whether it’s intellectually capable of beaming messages into space, the calculation of our chances of success no longer depends on uncertainties like the rareness of intelligence as an evolutionary outcome or the galactic popularity of radio technology. However, one of the biggest unknowns remains: the probability that life will arise in the first place on a rocky, watery, atmospheric planet like ours.

“Abiogenesis,” as the mystery event is called, seems to have occurred not long after Earth accumulated liquid water, leading some to speculate that life might start up readily, even inevitably, under favorable conditions. But if so, then shouldn’t abiogenesis have happened multiple times in Earth’s 4.5-billion-year history, spawning several biochemically distinct lineages rather than a monoculture of DNA-based life? John Baross, a microbiologist at the University of Washington who studies the origins of life, explained that abiogenesis might well have happened repeatedly, creating a menagerie of genetic codes, structures and metabolisms on early Earth. But gene-swapping and Darwinian selection would have merged these different upstarts into a single lineage, which has since colonized virtually every environment on Earth, preventing new upstarts from gaining ground. In short, it’s virtually impossible to tell whether abiogenesis was a fluke event, or a common occurrence — here, or elsewhere in the universe.

Scheduled to speak last at the symposium, Seager set a light-hearted tone for the after party. “I put it all in our favor,” she said, positing that life has a 100 percent chance of arising on Earth-like planets, and that half of these biospheres will produce detectable biosignature gases — another uncertainty in her equation. Crunching these wildly optimistic numbers yielded the prediction that two signs of alien life would be found in the next decade. “You’re supposed to laugh,” Seager said.

Meadows, Seager and their colleagues agree that the odds of such a detection this decade are slim. Though the prospects will improve with future missions, the James Webb telescope would have to get extremely lucky to pick a winner in its early attempts. And even if one of its targeted planets does harbor life, spectral measurements are easily foiled. In 2013, the Hubble Space Telescope monitored the starlight passing through the atmosphere of a midsized planet called GJ 1214b, but the spectrum was flat, with no chemical fingerprints at all. Seager and her collaborators reported in Nature that a high-altitude layer of clouds appeared to have obscured the planet’s sky from view.

Galaxy Simulations Offer a New Solution to the Fermi Paradox


Astronomers claim in a new paper that star motions should make it easy for civilizations to spread across the galaxy, but still we might find ourselves alone.

Art for "Galaxy Simulations Offer a New Solution to the Fermi Paradox "

As far as anyone knows, we have always been alone. It’s just us on this pale blue dot, “home to everyone you love, everyone you know, everyone you ever heard of,” as Carl Sagan so memorably put it. No one has called or dropped by. And yet the universe is filled with stars, nearly all those stars have planets, and some of those planets are surely livable. So where is everybody?

The Italian physicist Enrico Fermi was purportedly the first to pose this question, in 1950, and scientists have offered a bounty of solutions for his eponymous paradox since. One of the most famous came from Sagan himself, with William Newman, who postulated in a 1981 paper that we just need patience. Nobody has visited because they’re all too far away; it takes time to evolve a species intelligent enough to invent interstellar travel, and time for that species to spread across so many worlds. Nobody is here yet.

Other researchers have argued that extraterrestrial life might rarely become space-faring (just as only one species on Earth ever has). Some argue that tech-savvy species, when they arise, quickly self-destruct. Still others suggest aliens may have visited in the past, or that they’re avoiding us on purpose, having grown intelligent enough to be suspicious of everyone else. Perhaps the most pessimistic answer is a foundational paper from 1975, in which the astrophysicist Michael Hart declared that the only plausible reason nobody has visited is that there really is nobody out there.

Now comes a paper that rebuts Sagan and Newman, as well as Hart, and offers a new solution to the Fermi paradox that avoids speculation about alien psychology or anthropology.

The research, which is under review by The Astrophysical Journal, suggests it wouldn’t take as long as Sagan and Newman thought for a space-faring civilization to planet-hop across the galaxy, because the movements of stars can help distribute life. “The sun has been around the center of the Milky Way 50 times,” said Jonathan Carroll-Nellenback, an astronomer at the University of Rochester, who led the study. “Stellar motions alone would get you the spread of life on time scales much shorter than the age of the galaxy.” Still, although galaxies can become fully settled fairly quickly, the fact of our loneliness is not necessarily paradoxical: According to simulations by Carroll-Nellenback and his colleagues, natural variability will mean that sometimes galaxies will be settled, but often not — solving Fermi’s quandary.

The question of how easy it would be to settle the galaxy has played a central role in attempts to resolve the Fermi paradox. Hart and others calculated that a single space-faring species could populate the galaxy within a few million years, and maybe even as quickly as 650,000 years. Their absence, given the relative ease with which they should spread, means they must not exist, according to Hart.

Sagan and Newman argued it would take longer, in part because long-lived civilizations are likelier to grow more slowly. Faster-growing, rapacious societies might peter out before they could touch all the stars. So maybe there have been a lot of short-lived, fast-growing societies that wink out, or a few long-lived, slowly expanding societies that just haven’t arrived yet, as Jason Wright of Pennsylvania State University, a coauthor of the new study, summarized Sagan and Newman’s argument. But Wright doesn’t agree with either solution.

“That conflates the expansion of the species as a whole with the sustainability of individual settlements,” he said. “Even if it is true for one species, it is not going to be this iron-clad law of xenosociology where if they are expanding, they are necessarily short-lived.” After all, he noted, life on Earth is robust, “and it expands really fast.”

 

David Kaplan explores the best ways to search for alien life on distant planets.

Video: David Kaplan explores the best ways to search for alien life on distant planets.

Filming by Tom Hurwitz and Richard Fleming. Editing and motion graphics by Ryan Griffin. Other graphics and images from NASA, the European Southern Observatory and Creative Commons. Music by Podington Bear.

In their new paper, Carroll-Nellenback, Wright and their collaborators Adam Frank of Rochester and Caleb Scharf of Columbia University sought to examine the paradox without making untestable assumptions. They modeled the spread of a “settlement front” across the galaxy, and found that its speed would be strongly affected by the motions of stars, which previous work — including Sagan and Newman’s — treated as static objects. The settlement front could cross the entire galaxy based just on the motions of stars, regardless of the power of propulsion systems. “There is lots of time for exponential growth basically leading to every system being settled,” Carroll-Nellenback said.

But the fact that no interstellar visitors are here now — what Hart called “Fact A” — does not mean they do not exist, the authors say. While some civilizations might expand and become interstellar, not all of them last forever. On top of that, not every star is a choice destination, and not every planet is habitable. There’s also what Frank calls “the Aurora effect,” after Kim Stanley Robinson’s novel Aurora, in which settlers arrive at a habitable planet on which they nonetheless cannot survive.

When Carroll-Nellenback and his coauthors included these impediments to settlement in their model and ran many simulations with different star densities, seed civilizations, spacecraft velocities and other variations, they found a vast middle ground between a silent, empty galaxy and one teeming with life. It’s possible that the Milky Way is partially settled, or intermittently so; maybe explorers visited us in the past, but we don’t remember, and they died out. The solar system may well be amid other settled systems; it’s just been unvisited for millions of years.

Anders Sandberg, a futurist at the University of Oxford’s Future of Humanity Institute who has studied the Fermi paradox, said he thinks spacecraft would spread civilizations more effectively than stellar motions. “But the mixing of stars could be important,” he wrote in an email, “since it is likely to spread both life, through local panspermia” — the spread of life’s chemical precursors — “and intelligence, if it really is hard to travel long distances.”

Frank views his and his colleagues’ new paper as SETI-optimistic. He and Wright say that now we need to look harder for alien signals, which will be possible in the coming decades as more sophisticated telescopes open their eyes to the panoply of exoplanets and begin glimpsing their atmospheres.

“We are entering an era when we are going to have actual data relevant to life on other planets,” Frank said. “This couldn’t be more relevant than in the moment we live.”

Seth Shostak, an astronomer at the SETI Institute who has studied the Fermi paradox for decades, thinks it is likely to be explained by something more complex than distance and time — like perception.

Maybe we are not alone and have not been. “The click beetles in my backyard don’t notice that they’re surrounded by intelligent beings — namely my neighbors and me,” Shostak said, “but we’re here, nonetheless.”

Stephen Hawking’s final theory: untangling a peculiar black-hole paradox


The British theoretical physicist Stephen Hawking is perhaps best-known for his landmark work on black holes and, by extension, how they affect our understanding of the Universe. In the years before his death in 2018, he was still immersed in black hole theory, endeavouring to solve a puzzle that his own work had given rise to several decades earlier.

To put it succinctly, in the 1970s, Hawking discovered that black holes appear to be capable of destroying physical information – a characteristic very much at odds with contemporary quantum mechanics. Adapted from a 2016 paper that Hawking co-authored with the US theoretical physicist Andrew Strominger and the UK theoretical physicist Malcolm Perry, this animation offers a sophisticated-but-digestible – and frequently quite clever – visual presentation of Hawking’s final work, which proposes one potential solution to the ‘information paradox’.

Pluto Is Far in the Rearview. Next Stop: Ultima Thule


NASA’s New Horizons is poised to arrive at the most distant object ever seen up close—and there could be more to come

Pluto Is Far in the Rearview. Next Stop: Ultima Thule
Artist’s rendering of New Horizons as it sped past Pluto in 2015.

“Liftoff of NASA’s New Horizons spacecraft on a decade-long voyage to visit the planet Pluto and then beyond!”

On January 19, 2006 as the powerful 220-foot-tall Atlas V rocket, with the tiny interplanetary craft cradled in its largely empty nosecone, shot into the blue Florida sky, these words boomed out of loudspeakers, stirring the hearts and minds of the many thousands gathered at Cape Canaveral and many more watching over television and the internet. It was the fastest launch from Earth ever, because the payload was headed for the farthest objects ever targeted by a space probe. As the behemoth Atlas cleared the launch tower, those last three words—“and then beyond” —might not have attracted too much attention amongst all the Plutomania, but now, nearly 13 years later, we are all about to find out what that meant.

The Kuiper Belt—the vast, distant repository of millions of frozen, primitive objects, had been theorized but not yet found when a mission to Pluto was first studied by NASA in 1990. Its discovery in the early 1990s showed that Pluto was not just an oddity at the outer edge of the solar system but part of an entirely unexplored territory beyond the orbit of Neptune. This discovery helped to marshal scientific support for a mission that was recast as an expedition to Pluto and the Kuiper Belt.

In our sci-fi fantasy shows, the spaceships of future centuries are always general-purpose, able to travel anywhere their intrepid captains direct. In the 21st century we’re still in an age where our deep space craft are single-use, designed to go only to specific targets, which they often carry barely enough fuel and resources to reach. A few times we’ve been able to send some of our craft on an added “extended” mission to visit another comet or asteroid.

Yet one of the many exceptional features of New Horizons is that it was designed, from the beginning, to keep going after Pluto and to explore further worlds that had not even been identified when it was launched. This was necessary because at liftoff, there was no known Kuiper Belt object that New Horizons could reach after visiting Pluto. However, our statistical knowledge about the Kuiper Belt suggested there should be many such objects, which might be discovered while New Horizons was en route. Once that happened, New Horizons would be re-directed to visit one of them.

This search did not go as planned. It turned out to be much harder than anticipated to find a post-Pluto destination. This was largely because, the way things lined up, the area of the sky that needed to be explored was near the center of the Milky Way galaxy—the worst possible celestial real estate to look for new, faint objects against the dense population of background stars. As New Horizons made its nine-year journey clear across the solar system, years of looking with the best ground-based telescopes failed to reveal a suitable object. It got to the point where the success of the extended Kuiper Belt mission was in real doubt.

Only an unplanned search with the Hubble Space Telescope could plausibly save the day. In June, 2014, just a year before the Pluto encounter, the Hubble was pressed into service and the New Horizons team managed to find two objects their craft could visit with available fuel. Of these, the object MU69, now nicknamed Ultima Thule (a Greek-Latin hybrid meaning “beyond the known world”), was on a more favorable orbit to intercept.

So now, ever since rounding Pluto in July 2015, and revealing that dwarf planet and its 5 moons to us in all their surprising, variegated glory, New Horizons has been making a beeline towards Ultima Thule, which orbits another billion miles farther from Earth than Pluto. On New Year’s Eve, heading into 2019, Ultima Thule will become by far the farthest world ever explored by human craft, as New Horizons, having traveled for three and a half more years through the cold, black yonder of the Kuiper Belt, skims within a few thousand miles of its surface.

The closest approach will come 33 minutes after midnight East Coast time, yet news of success or failure will not reach Earth until the following morning. At four billion miles, the unprecedented distance of this encounter also means a much greater communications delay than any previous flyby: it will take 12 hours for a round trip at the speed of light between Earth and the spacecraft. While it is executing its last maneuvers, the spacecraft will truly be on its own. The synchronization with our calendrical page turning is completely serendipitous but should make for an especially celebratory encounter: Finally, a real reason to stay up past midnight on New Year’s Eve!

Never has there been the prospect of going so quickly from ignorance to relative clarity about an entirely new type of solar system object. Usually we head into a flyby encounter knowing much more about our target than we do now about Ultima Thule. All we know is its rough size (about 20 miles across), that it seems to have a double-lobed shape, that it may even be two separate objects circling one another and that its overall color is a bit redder than Pluto.

Because it is so distant, small and dark, we don’t even have any detailed spectral clues as to its surface composition. And because it is such a small target and New Horizons is moving so quickly, not until a couple of days before the encounter will it even be resolvable into multiple pixels. Even compared to other first flybys, which are always hectic bursts of discoveries, this one will happen quickly.

The same suite of seven precision scientific instruments that three years ago revealed Pluto to us will now be used to make a quick but detailed study of Ultima and its environment. Is it heavily cratered? Uniform or varied? Rough or smooth? Rocky or icy? Soon we’ll have answers and clues, not just to the history of this one mysterious object but toward a new understanding of the solar system’s lost origin story. For the Kuiper Belt is the distant construction warehouse of the solar system, the place where leftover building materials from making the planets have been kept in a cool, dry place. Up until now it has been off-limits, waiting for someone curious and clever enough to make it out there and discover what relics it holds of the original materials and processes with which the planets were built.

With the Pluto encounter, the last of the classically known planets made the transition from speck to world, from telescopic point to finely photographed landscape. With the rapidly approaching flyby of Ultima Thule, another immense realm of our solar system will be transformed from the astronomical study only of distant unresolved dots to the geological study of the surface, shape and history of variegated bodies.

This will be our first close-up observation of such a distant object and may well be our last for many years or even decades. But maybe not. Since the Pluto flyby, interest in possible new Kuiper Belt missions has grown, and the new results from Ultima may add momentum. It may even be possible for New Horizons to visit more objects in its continuing traverse across the Kuiper Belt. Fuel is limited but some redirection is possible. The nuclear batteries are slowly decaying, but the spacecraft should be operable and maintain communications with Earth for well over another decade. New Horizons’ onboard telescopic camera can be used to search for more targets in its path.

With a little luck, this well-traveled spacecraft may yet find another world to visit before it heads off to wander the galaxy forever, a derelict spacecraft that has completed its mission, a relic of 21st-century human curiosity and daring.

Earthrise, a photo that changed the world


December 24 is the 50th anniversary of Earthrise, arguably one of the most profound images in the history of human culture. When astronaut William Anders photographed a fragile blue sphere set in dark space peeking over the Moon, it changed our perception of our place in space and fuelled environmental awareness around the world.

The photo let us see our planet from a great distance for the first time. The living Earth, surrounded by the darkness of space, appears fragile and vulnerable, with finite resources.


 

Viewing a small blue Earth against the black backdrop of space, with the barren moonscape in the foreground, evokes feelings of vastness: we are a small planet, orbiting an ordinary star, in an unremarkable galaxy among the billions we can observe. The image prompts emotions of insignificance – Earth is only special because it’s the planet we live on.

As astronaut Jim Lovell said during the live broadcast from Apollo 8, “The vast loneliness is awe-inspiring, and it makes you realise just what you have back there on Earth.”

The Apollo 8 Christmas Eve broadcast.

Earthrise is a testament to the extraordinary capacity of human perception. Although, in 1968, the photograph seemed revelatory and unexpected, it belongs to an extraordinary history of representing the Earth from above. Anders may have produced an image that radically shifted our view of ourselves, but we were ready to see it.

A history of flight

People have always dreamed of flying. As we grew from hot-air balloons to space shuttles, the camera has been there for much of the ride.

After WWII, the US military used captured V-2 rockets to launch motion-picture cameras out of the atmosphere, producing the first images of Earth from space.

Russia’s Sputnik spurred the United States to launch a series of satellites — watching the enemy and the weather — and then NASA turned its attention to the Moon, launching a series of exploratory probes. One (Lunar Orbiter I, 1966) turned its camera across a sliver of the Moon’s surface and found the Earth, rising above it.

The non-human version of Earthrise from Lunar Orbiter in 1966. NASA

Despite not being the “first” image of the Earth from our Moon, Earthrise is special. It was directly witnessed by the astronauts as well as being captured by the camera. It elegantly illustrates how human perception is something that is constantly evolving, often hand in hand with technology.

Earthrise showed us that Earth is a connected system, and any changes made to this system potentially affect the whole of the planet. Although the Apollo missions sought to reveal the Moon, they also powerfully revealed the limits of our own planet. The idea of a Spaceship Earth, with its interdependent ecologies and finite resources, became an icon of a growing environmental movement concerned with the ecological impacts of industrialisation and population growth.

‘Spaceship Earth’ became a powerful rallying cry for environmental groups.

From space, we observe the thin shield provided by our atmosphere, allowing life to flourish on the surface of our planet. Lifeforms created Earth’s atmosphere by removing carbon dioxide and generating free oxygen. They created an unusual mix of gases compared to other planets – an atmosphere with a protective ozone layer and a mix of gases that trap heat and moderate extremes of temperature. Over millions of years, this special mix has allowed a huge diversity of life forms to evolve, including (relatively recently on this time scale) Homo sapiens.

The field of meteorology has benefited enormously from the technology foreshadowed by the Earthrise photo. Our knowledge is no longer limited to Earth-based weather-observing stations.

Satellites can now bring us an Earthrise-type image every ten minutes, allowing us to observe extremes such as tropical cyclones as they form over the ocean, potentially affecting life and land. Importantly, we now possess a long enough record of satellite information so that in many instances we can begin to examine long-term changes of such events.

Tropical Cyclone Owen seen from space. 

The human population has doubled in the 50 years since the Earthrise image, resulting in habitat destruction, the spread of pest species and wildfires spurred by climate warming. Every year, our actions endanger more species.

Earth’s climate has undergone enormous changes in the five decades since the Earthrise photo was taken. Much of the increase in Australian and global temperatures has happened in the past 50 years. This warming is affecting us now, with an increase in the frequency of extreme events such as heatwaves, and vast changes across the oceans and polar caps.


 

With further warming projected, it is important that we take this chance to look back at the Earthrise photo of our little planet, so starkly presented against the vastness of space. The perspective that it offers us can help us choose the path for our planet for the next 50 years.

It reminds us of the wonders of the Earth system, its beauty and its fragility. It encourages us to continue to seek understanding of its weather systems, blue ocean and ice caps through scientific endeavour and sustained monitoring.

The beauty of our planet as seen from afar – and up close – can inspire us to make changes to secure the amazing and diverse animals that share our Earth.

Zoos become conservation organisations, holding, breeding and releasing critically endangered animals. Scientists teach us about the capacities of animals and the threats to their survival.

Communities rise to the challenge and people in their thousands take actions to help wildlife, from buying toilet paper made from recycled paper to not releasing balloons outdoors. If we stand together we can secure a future for all nature on this remarkable planet.



But is a 50-year-old photo enough to reignite the environmental awareness and action required to tackle today’s threats to nature? What will be this generation’s Earthrise moment?

A NASA probe is going to visit Ultima Thule, the farthest object humanity has ever tried to reach, on New Year’s Day


ultima thule new horizons 2014 mu69 kuiper belt nasa jhuapl swri steve gribben
An illustration of NASA’s New Horizons probe visiting 2014 MU69, a Kuiper Belt object that exists about 1 billion miles beyond Pluto.
 
  • NASA’s New Horizons probe, which visited Pluto in 2015, is closing in on a mysterious object called Ultima Thule.
  • New Horizons will fly past Ultima Thule, formally known as 2014 MU69, on New Year’s Day.
  • Ultima Thule will be the most distant object humanity has ever visited if the flyby goes as planned.
  • The nuclear-powered spacecraft will take hundreds photos of the space rock.
  • The flyby is “about 10,000 times” more challenging than visiting Pluto, the mission’s leader said.

NASA scientists are about to make history by flying a probe past a mysterious, mountain-size object beyond the orbit of Pluto.

If the flyby goes as planned, it will be the most distant object in space that humanity has ever tried to visit.

NASA’s nuclear-powered New Horizons spacecraft will attempt the maneuver on New Year’s Day. The object the probe is approaching is called Ultima Thule (pronounced “tool-ee”) or 2014 MU 69, as it’s formally known.

NASA didn’t know Ultima Thule existed when New Horizons launched toward Pluto in 2006. There wasn’t even a reliable way to detect it until after astronauts flew out to the Hubble Space Telescope in May 2009 and plugged in an upgraded camera.

Hubble first definitively photographed Ultima Thule in June 2014 — about a year before New Horizons flew past Pluto. Now, 4 billion miles away from Earth, New Horizons has the object in its sights.

The deep uncertainty about Ultima Thule makes planetary science researchers like Alan Stern, who leads the New Horizons mission, all the more excited about the flyby.

“If we knew what to expect, we wouldn’t be going to Ultima Thule. It’s an object we’ve never encountered before,” Stern told Business Insider. “This is what what exploration is about.”

Where and what the heck is Ultima Thule?

kuiper belt objects kbos pluto new horizons flight path ultima thule 2014 mu69 alex parker jhuapl swri
An illustration of Kuiper Belt Objects (dots) with New Horizons’ flight path (yellow), Pluto, and Ultima Thule/2014 MU69.

New Horizons is coasting through a zone called the Kuiper Belt, a region where sunlight is about as weak as the light from a full moon. That far away, frozen leftovers of the solar system’s formation — Kuiper Belt Objects, or KBOs — lurk in vast numbers (including Pluto).

Ultima Thule is one of these pristine remnants. It has presumably remained in its distant and icy orbit for billions of years, and it is not a planet that has deformed under its own mass and erased its early history. This means studying it may help reveal how the solar system evolved to form planets like Earth, Stern said.

“Ultima is the first thing we’ve been to that is not big enough to have a geological engine like a planet, and also something that’s never been warmed greatly by the sun,” he said. “It’s like a time capsule from 4.5 billion years ago. That’s what makes it so special.”

Stern added that the flyby will be the astronomical equivalent of an archaeological dig in Egypt.

“It’s like the first time someone opened up the pharaoh’s tomb and went inside, and you see what the culture was like 1,000 years ago,” he said. “Except this is exploring the dawn of the solar system.”

asteroids asteroid field star nasa jpl 717846main_pia16610_full
An artist’s rendering of planetesimals.

Stern considers Ultima Thule to be a “planetesimal” or seed that might have formed a planet if it had acquired enough material.

“It’s a building block of larger planets, or a planetary embryo,” Stern said. “In that sense, it’s like a paleontologist finding the fossilized embryo of a dinosaur. It has a very special value.”

In New Horizons’ first images, researchers will pay close attention to the outward appearance of Ultima Thule. Learning whether the surface is relatively smooth or features a mix of pebbles, huge boulders, cliffs, and other features will yield clues about how planets form.

Each bit of image data from New Horizons, moving at the speed of light as radio waves, will take about six hours to reach antennas on Earth.

Journey into the unknown

In June, New Horizons woke up from half a year of hibernation to begin zeroing in on Ultima Thule.

After a series of checks, mission managers in October fired the probe’s engine to put it on a more precise path to Ultima Thule.

This week, researchers finished confirming that there are no obvious moons, debris fields, or other objects floating in the flight path of New Horizons (and that it might slam into), so they kept the robot on-course for its historic encounter.

The flyby is slated to begin late on New Year’s Eve. New Horizons will start taking hundreds of photos in a highly choreographed, pre-programmed sequence.

“Rendezvousing with something the size of a large, filthy mountain covered in dirt, a billion miles away from Pluto, and honing in on it is about 10,000 times harder than reaching Pluto,” Stern said. “That’s because it’s about 10,000 times smaller. The achievement of getting to it is unbelievable.”

The target of New Horizons’ cameras and other instruments won’t just be Ultima Thule itself, either.

“We’re plastering all of the space around it for moons, rings, and even an atmosphere,” Stern said. “If any of those things are there, we’ll see them.”

new horizons rtg NASA

At 12:33 a.m. ET on New Year’s Day, the space probe will be its closest point — about 2,175 miles— to the mountain-size object. New Horizons will also turn around to photograph its exit at a speed of 35,000 mph.

Stern said the initial images will each take two hours to transmit, and the first ones will be released early in the day on January 2.

However, those early photos will be small (as they were for Pluto). It will take months to receive the most detailed, full-resolution images due to the power, antenna, and other physical limitations of the spacecraft. The first full-resolution images won’t arrive until February.

Stern, who recently helped write a book titled “Chasing New Horizons: Inside the Epic First Mission to Pluto,” said Ultima Thule got its name from a Norse phrase that means “beyond the farthest frontiers.” He shied away from making any predictions about what the images might show, citing how shocking the first close-up pictures of Pluto were.

“I don’t know what we’re going to find,” he said. “If it’s anything as surprising as Pluto, though, it will be wonderful.”

How to watch live coverage of New Horizons’ flyby of Ultima Thule

New Horizons control room
Members of the New Horizons science team react to seeing the spacecraft’s last and sharpest image of Pluto before closest approach

Those interested in watching expert commentary about the flyby and seeing if it succeeded can tune into a live broadcast on New Year’s Day.

Michael Buckley, a spokesperson for Johns Hopkins University’s Applied Physical Laboratory (which hosts the New Horizons mission for NASA), said the lab’s YouTube channel will stream a video feed of the moment scientists learn that the spacecraft made it past Ultima Thule.

The show will go on even if President Donald Trump’s government shutdown over border wall funding silences NASA TV into 2019.

“We’re still planning one going ahead with the programming that we’ve scheduled,” Buckley told Business Insider. “The biggest change is that we wouldn’t be using any NASA platforms.”

He said live coverage is expected to begin on January 1 around 9:30 a.m. EST, and the “ok” signal from New Horizons should arrive after 10 a.m. EST.

Navigating NASA’s first mission to the Trojan asteroids


This diagram illustrates Lucy’s orbital path. The spacecraft’s path (green) is shown in a frame of reference where Jupiter remains stationary, giving the trajectory its pretzel-like shape.

In science fiction, explorers can hop in futuristic spaceships and traverse half the galaxy in the blink of a plot hole. However, this sidelines the navigational acrobatics required in order to guarantee real-life mission success.

In 2021, the feat of navigation that is the Lucy mission will launch. To steer Lucy towards its targets doesn’t simply involve programming a map into a spacecraft and giving it gas money – it will fly by six asteroid targets, each in different orbits, over the course of 12 years.

Lucy’s destination is among Jupiter’s Trojan asteroids, clusters of rocky bodies almost as old as the Sun itself, and visiting these asteroids may help unlock the secrets of the early solar system. Lucy will encounter a Main Belt asteroid in 2025, where it will conduct a practice run of its instruments before encountering the first four Trojan targets from 2027-2028. In 2033, Lucy will end its mission with a study of a binary system of two Trojans orbiting each other.

Getting the spacecraft where it needs to go is a massive challenge. The solar system is in constant motion, and gravitational forces will pull on Lucy at all times, especially from the targets it aims to visit. Previous missions have flown by and even orbited multiple targets, but none so many as will Lucy.

Scientists and engineers involved with trajectory design have the responsibility of figuring out that route, under Flight Dynamics Team Leader Kevin Berry of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. One such engineer is Jacob Englander, the optimization technical lead for the Lucy mission. “There are two ways to navigate a mission like Lucy,” he said. “You can either burn an enormous amount of propellant and zig-zag your way around trying to find more targets, or you can look for an opportunity where they just all happen to line up perfectly.” To visit these aligned targets, the majority of Lucy’s high-speed lane changes will come from gravity assists, with minimal use of fueled tweaks.

Though Lucy is programmed to throw itself out into a celestial alignment that will not occur for decades, it cannot be left to its own devices. Once the spacecraft begins to approach its asteroid targets, optical navigation is the next required step.

“OpNav,” as optical navigation technical lead Coralie Adam refers to it, is the usage of imagery from the on-board cameras to determine Lucy’s position relative to the . This is a useful measurement used by the navigation team to tweak Lucy’s route and ensure it stays on the nominal flyby path. Adam works in Simi Valley, California, with KinetX, the company NASA selected to conduct Lucy’s deep space navigation.

By using the communications link from the spacecraft to Earth, Adam said, the Lucy team gets information about the spacecraft’s location, direction and velocity. The spacecraft takes pictures and sends them down to Earth, where Adam and other optical navigators use software to determine where the picture was taken based on the location of stars and the target. The orbit determination team uses this data along with data from the communications link to solve for where the spacecraft is and where it is expected to be, relative to the Trojans. The team then designs a to get Lucy on track. “The first maneuver is tiny,” said navigation technical lead Dale Stanbridge, who is also of KinetX. “But the second one is at 898 meters per second. That’s a characteristic of Lucy: very large delta V maneuvers.” Delta V refers to the change in speed during the maneuver.

Communicating all of these navigation commands with Lucy is a process all on its own. “Lockheed Martin sends the commands to the spacecraft via the Deep Space Network,” Adam said. “What we do is we work with Lockheed and the Southwest Research Institute, where teams are sequencing the instruments and designing how the spacecraft is pointed, to make sure Lucy takes the pictures we want when we want them.”

“The maneuvers to correct Lucy’s trajectory are all going to be really critical because the spacecraft must encounter the Trojan at the intersection of the spacecraft and Trojan orbital planes,” Stanbridge said. “Changing the spacecraft orbital plane requires a lot of energy, so the maneuvers need to be executed at the optimal time to reach to next body while minimizing the fuel cost.”

While Lucy is conducting deep space maneuvers to correct its trajectory toward its targets, communications with the spacecraft are sometimes lost for brief periods. “Blackout periods can be up to 30 minutes for some of our bigger maneuvers,” Stanbridge said. “Other times you could lose communications would be when, for example, the Sun, comes between the Earth tracking station and the spacecraft, where the signal would be degraded by passing through the solar plasma.”

Losing contact isn’t disastrous, though. “We have high-fidelity predictions of the spacecraft trajectory which are easily good enough to resume tracking the spacecraft when the event causing a communication loss is over,” Stanbridge said.

What route will Lucy take once its mission is complete, nearly 15 years from now? “We’re just going to leave it out there,” Englander said. “We did an analysis to see if it passively hits anything, and looking far into the future, it doesn’t.” The Lucy team has given the a clear path for thousands of years, long after Lucy has rewritten the textbooks on our solar system’s history.

Read more at: https://phys.org/news/2018-12-nasa-mission-trojan-asteroids.html#jCp

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