Tag: exoplanets

A Frozen Super-Earth Is Close But You Won’t Want To Visit It

Night by night, star by star, astronomers are edging ever closer to learning just how crowded our universe really is—or at least our galaxy, anyway.

A quarter century after the first exoplanets were found orbiting other stars, statistics from the thousands now known have revealed that, on average, each and every stellar denizen of the Milky Way must be accompanied by at least one world.

Look long and hard enough for a planet around any given star in our galaxy and you are practically guaranteed to find something sooner or later.

But even a crowded universe can be a lonely place. Our planet-rich Milky Way may prove to be life-poor. Of all the galaxy’s known worlds, only a figurative handful resemble Earth in size and orbit.

Each occupying a nebulous “Goldilocks” region of just-rightness—a fairy-tale-simple ideal in which a world is neither too big nor too small, neither too hot nor too cold, to sustain liquid water and life on its surface.

Instead, most of the Milky Way’s planets are worlds theorists failed to predict and have yet to fit comfortably in any conception of habitability: “super-Earths” bigger than our familiar planet but smaller than Neptune.

No super-Earths twirl around our sun for solar system–bound scientists to directly study, making it that much harder to know whether any elsewhere are Goldilocks worlds—or, for that matter, whether any one-size-fits-all metric of habitability is hopelessly naive.




A Frozen Super-Earth?

If you live in a city of millions of people, you are not interested in meeting every one of them—but maybe you want to meet your immediate neighbors,” says lead author Ignasi Ribas, an astronomer at the Institute of Space Studies of Catalonia in Spain.

“This is what we are doing for the planetary systems of the stars that surround us. Otherwise we cannot answer the big questions. How does our solar system and our Earth fit in with the rest of the galaxy?

“Are there other habitable or inhabited planets? Barnard’s Star b is not giving us those answers just yet, but it is telling us part of the story we need to know.”

Located in the constellation of Ophiuchus, Barnard’s Star is so dim in visible light that it cannot be seen with unaided eyes.

Yet it has been a favorite of astronomers since 1916, when measurements revealed its apparent motion across the sky was greater than that of any other star relative to our sun.

A sign of its extremely close cosmic proximity. The star’s nearness to us is only temporary—within tens of thousands of years, its trajectory will have swept it out of our solar system’s list of top five closest stars.

According to Ribas and his colleagues, the candidate planet is at least three times heavier than our own, and circles its star in a 233-day orbit.

That would put it in the torrid orbital vicinity of Venus around our yellow sun, but Barnard’s Star is a comparatively pint-size and dim red dwarf star.

This means its newfound companion is near the “snow line,” the boundary beyond which water almost exclusively exists as frozen ice—a region around other stars thought to be chock-full of planets, but that astronomers have only just begun to probe for small worlds.

Alternatively, the planet might be covered by a thick, insulating blanket of hydrogen leftover from its birth in a spinning disk of gas and dust around its star.

Although hydrogen on smaller, hotter worlds would dissipate into space, super-Earths in frigid orbits might manage to hang on to enough of the gas to build up a massive planet-warming greenhouse effect—a possibility that throws Earth-centric Goldilocks ideas into tumult.

If this mechanism operates on Barnard’s Star b or other cold super-Earths, “our dreams that every star may have a habitable planet could well come true,” says Sara Seager, a planet-hunting astrophysicist at Massachusetts Institute of Technology who was not involved with Ribas’s study.

“There are some crazy worlds out there.”

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Two Big NASA Space Missions Ended This Week, But Don’t Panic

It’s easy for a superstitious mind to jump to anxious conclusions from this week, after NASA announced the end of two long-running missions: the exoplanet-hunting Kepler space telescope and the Dawn mission that visited the asteroid belt.

And those high-profile finales come in the midst of a spree of other spacecraft troubles: the Opportunity rover on Mars remains silent nearly five months after a planet-engulfing dust storm, and the Hubble Space Telescope and Chandra X-Ray Observatory were both briefly offline in October.

But as NASA personnel stressed during a news conference Tuesday (Oct. 30) to announce the end of the Kepler mission, the sudden spurt of bad news is no reason to panic.

We always try to get as much science as we can out of our spacecraft,” Paul Hertz, NASA’s head of astrophysics in the Science Mission Directorate, said during the news conference, adding that the agency has more than 60 science spacecraft at work right now.

If you only pick out the ones that are getting toward the end of their life then you can make a story, but if you look at the entire portfolio of spacecraft, I don’t think we have a problem at all, I think we are in a golden age of NASA science,” Hertz said.

Both the Kepler telescope, which identified more than 2,600 alien planets, and the Dawn spacecraft, which visited the asteroid Vesta and the dwarf planet Ceres, ended because they no longer had enough gas in the tank.




Engineers on both missions knew their ends were looming, since they could calculate remaining fuel estimates.

Both spacecraft used chemical fuel to twist themselves back toward Earth and beam their findings home; without that fuel there was no way to learn from our distant emissaries.

Sure, each mission could theoretically have been stocked with more fuel, but not without fattening their price tags.

And both missions lasted far longer than they were initially designed to endure, overcoming serious mechanical problems along the way.

When the Kepler mission began in April 2009, it was originally designed to last three years — instead, it lasted until 2013, when two broken reaction wheels forced its original mission to end.

The telescope’s engineers still didn’t abandon it; instead, they reprogrammed it, so that rather than look for exoplanets in one particular patch of the sky, it hopped from region to region.

Reincarnated, the telescope completed another four years of observations.

Dawn also survived reaction-wheel failures that threatened to sideline the spacecraft at the end of its stay at the asteroid Vesta.

In Dawn’s case, engineers rescued it by using fuel to make small adjustments to its position.

This spacecraft also blew past its original timeline, spending 14 months at Vesta instead of the scheduled seven and more than three years at the dwarf planet Ceres instead of the scheduled five months.

Although the fate of the Opportunity rover remains unknown as NASA continues to try to revive it through January, the rover has outpaced its goals just as dramatically as its spacefaring cohorts.

Its mission was originally scheduled to last just 90 Martian days, each about 40 minutes longer than a terrestrial one. Instead, the rover has puttered the Red Planet for more than 14 years.

Beyond the casualty list, NASA also has some beginnings worth remembering. Its Transiting Exoplanet Survey Satellite, or TESS, picked up where Kepler left off, beginning observations in late July, and has already identified multiple possible planets.

The Parker Solar Probe mission to “touch the sun” launched in August and is making its first close approach to our star this week.

NASA’s new Mars lander, called InSight, will touch down just after Thanksgiving, ready to study the Red Planet’s interior, and the New Horizons spacecraft will ring in the new year by swinging past a distant Kuiper Belt object.

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NASA’s Revolutionary Planet-Hunting Telescope Kepler Runs Out of Fuel

NASA’s prolific Kepler Space Telescope has run out of fuel, agency officials announced on Oct. 30, 2018. The planet-hunting space telescope discovered thousands of alien worlds around distant stars since its launch in 2009.

The most prolific planet-hunting machine in history has signed off.

NASA’s Kepler space telescope, which has discovered 70 percent of the 3,800 confirmed alien worlds to date, has run out of fuel, agency officials announced last October 30.

Kepler can no longer reorient itself to study cosmic objects or beam its data home to Earth, so the legendary instrument’s in-space work is done after nearly a decade.

And that work has been transformative.

“Kepler has taught us that planets are ubiquitous and incredibly diverse,” Kepler project scientist Jessie Dotson, who’s based at NASA’s Ames Research Center in Moffett Field, California said.




“It’s changed how we look at the night sky.”

The announcement was not unexpected. Kepler has been running low on fuel for months, and mission managers put the spacecraft to sleep several times recently to extend its operational life as much as possible.

But the end couldn’t be forestalled forever; Kepler’s tank finally went dry two weeks ago, mission team members said during a telecon with reporters today.

This marks the end of spacecraft operations for Kepler, and the end of the collection of science data,” Paul Hertz, head of NASA’s Astrophysics Division, said during the telecon.

Prepping the Kepler spacecraft pre-launch in 2009.

Even though Kepler has closed its eyes, discoveries from the mission should keep rolling in for years to come.

About 2,900 “candidate” exoplanets detected by the spacecraft still need to be vetted, and most of those should end up being the real deal, Kepler team members have said.

A lot of other data still needs to be analyzed as well, Dotson stressed.

And Kepler will continue to live on in the exoplanet revolution it helped spark.

For example, in April, NASA launched a new spacecraft called the Transiting Exoplanet Survey Satellite (TESS), which is hunting for alien worlds circling stars that lie relatively close to the sun (using the transit method, just like Kepler).

Kepler’s death “is not the end of an era,” Kepler system engineer Charlie Sobeck, also of NASA Ames said. “It’s an occasion to mark, but it’s not an end.”

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We Could Find Aliens by Spotting Their Satellites

Alien civilizations with technology on a par with humanity’s could be detectable using today’s instruments.

A new study suggests that if geostationary satellites are thick enough around an alien world, they could be spotted with telescopes already hunting for undiscovered planets.

Both governments and private corporations on our own world use geostationary satellites — which orbit such that they hover over the same spot on Earth — for science, communications, espionage and military applications.

If advanced alien civilizations loft enough satellites into their own geostationary belts, these spacecraft could create a dense, ring-like structure visible from Earth, according to the study.

Socas-Navarro simulated the presence of belts of geostationary satellites around exoplanets, to see whether they could be detected by instruments like NASA’s Kepler space telescope and the agency’s recently launched Transiting Exoplanet Survey Satellite (TESS).

He found that the belt would need to be about 0.01 percent full for such spacecraft to detect it, whether populated by many small satellites or a handful of large, city-size objects.

We just need to look for the right signature in the data,” he said.

Socas-Navarro calls this hypothetical structure the Clarke exobelt (CEB), after famed sci-fi author Arthur C. Clarke.




Both Kepler and TESS detect planets using what’s known as the transit method. The spacecraft watch a field of stars for an extended amount of time.

If a planet has the right orbit, and the timing is right, that world will pass in front of its host star from the telescope’s perspective, causing a small, potentially detectable dip in brightness.

In addition to working as an astrophysicist, Socas-Navarro hosts a weekly radio show and podcast. That work helped him come up with the Clarke exobelt idea, he said.

One day, a listener asked about a geostationary satellite for the sun.

Sufficient material orbiting an exoplanet causes a small dip in starlight before and after the body of the world makes its transit. Scientists have used this method to discover rings around planets outside the solar system and even around distant solar system bodies.

Socas-Navarro said the putative alien-satellite signal would have a signature similar to that of rings — both an exobelt and rings are made up of a swarm of objects orbiting a planet — but there are subtle technical differences in how that signature would look.

The signal would also reveal the altitude of the orbiting objects, which could provide a significant clue as to whether the objects were natural or alien-made.

A ring system can occur at any number of distances from the surface of the planet. But if the objects orbited at a planet’s geostationary height — about 22,200 miles (35,700 kilometers) — they are “almost certainly artificial,” Socas-Navarro said.

Similarly, a massive space city or a large station close to a space elevator could look like an exomoon. Again, Socas-Navarro said, altitude is key. If the object hovers at geostationary height, it’s likely to be artificial.

It doesn’t seem to matter too much if they are many small or [a] few large [objects],” he said. “As long as they are spread out all over the orbit, they will basically produce the same signature.

He also found that the ideal conditions to spot such a satellite belt would be around dim red dwarf stars located within 100 light-years of Earth.

The new study was published last month in The Astrophysical Journal. You can read it for free at the online preprint server arXiv.org.

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Astronomers May Have Discovered The First Moon Ever Found Outside Our Solar System

An artistic rendering of the Kepler-1625b planetary system.

A pair of astronomers believes they’ve found a moon orbiting a planet outside our Solar System — something that has never before been confirmed to exist.

Though they aren’t totally certain of their discovery yet, the find opens up the possibility that more distant moons are out there. And that could change our understanding of how the Universe is structured.

The astronomy team from Columbia University found this distant satellite, known as an exomoon, using two of NASA’s space telescopes.

They first spotted a signal from the object in data collected by the planet-hunting telescope Kepler, and then they followed up with the Hubble Space Telescope, which is in orbit around Earth.

Thanks to the observations from these two spacecraft, the team suspect this moon orbits around a Jupiter-sized planet located about 4,000 light-years from Earth. And this planet, dubbed Kepler-1625b, orbits around a star similar to our Sun.

Scientists have strongly believed for decades that moons exist outside our Solar System, but these objects have remained elusive for scientists up until now.




There have been just a couple of candidates that astronomers have speculated about in the past, but nothing has been confirmed.

That’s because moons are thought to be too small and too faint to pick up from Earth. However, this suspected exomoon, detailed today in the journal Science Advances, is particularly large, about the size of Neptune, making it one of the few targets that our telescopes can detect.

You can make the argument that this is the lowest hanging fruit,” Alex Teachey, an astronomy graduate student at Columbia University and one of the lead authors on the paper said.

“Because it is so large, in some ways, this is the first thing we should detect because it is the easiest.”

Teachey argues that finding more moons outside our Solar System will change our understanding of how planetary systems formed thousands of light-years away.

Our cosmic neighborhood is filled with moons, and they explain a lot about how our planets came to be. Exomoons could tell similar tales.

NASA’s Hubble Space Telescope.

However, none of our moons come close to the size of this one, which creates a puzzle for astronomers.

Because it is so unusual, or at least has not been anticipated largely by the community, this poses new challenges to explain it,” says Teachey. “How do you get something like this?

It was only a few decades ago — in the late 1980s and early 1990s — that astronomers confirmed the existence of planets outside our Solar System.

Since then, thousands of these distant worlds, known as exoplanets, have been confirmed by spacecraft like Kepler and other telescopes.

Perhaps the most popular way to find exoplanets is by staring at stars, waiting for them to flicker. When a planet crosses “in front” of its host star, it dims the stars’ light ever so slightly.

These dips in brightness can be used to determine how big a planet is and the kind of orbit it’s on.

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NASA’s New Planet Hunter Has Already Spotted Two Candidates For Earth-Like Alien Worlds

 

NASA’s Transiting Exoplanet Survey Satellite (TESS) has only been on the job less than two months, and already it’s ponying up the planet goods.

The exoplanet-hunting space telescope has found two candidate planets, and there are plenty more on the horizon.

The two candidate planets are called Pi Mensae c, orbiting bright yellow dwarf star Pi Mensae, just under 60 light-years from Earth; and LHS 3844 b, orbiting red dwarf star LHS 3844, just under 49 light-years away.

TESS took its first test observations on July 25 (and managed to get some pretty great snaps of a passing comet), and its first official science observations began on August 7.

However, it was observing a large swathe of sky from the moment it opened its eyes – four optical cameras – and both discoveries are based on data from July 25 to August 22.

So far, they are only candidate planets, yet to be validated by the final review process. If they pass that test, they’ll go down in history as TESS’s first two discoveries. Here’s what we know so far about them.

Both planets appear to be Earth-like and rocky, but neither is habitable according to our guidelines – both are too close to their stars for liquid water.

Pi Mensae c, the first planet announced, is a super-Earth, clocking in at just over twice the size of Earth. It’s really close to Pi Mensae – it orbits the star in just 6.27 days.




A preliminary analysis indicates that the planet has a rocky iron core, and also contains a substantial proportion of lighter materials such as water, methane, hydrogen and helium – although we’ll need a more detailed survey to confirm that.

It also has a sibling – it’s not the first object to be found orbiting Pi Mensae. That honour goes to Pi Mensae b, an enormous planet with 10 times the mass of Jupiter discovered in 2001.

It’s much farther out than Pi Mensae c, on an orbit of 2,083 days. LHS 3844 b is a little bit smaller, classified as a “hot Earth“.

It’s just over 1.3 times the size of Earth, and on an incredibly tight orbit of just 11 hours. Since the two are so close together, it’s highly likely the planet is blasted with too much stellar radiation to retain an atmosphere.

TESS does need a bit of time to collect enough data for identifying an exoplanet.

Like its predecessor Kepler, it uses what is known as the transit method for detection – scanning and photographing a region of the sky multiple times, looking for changes in the brightness of stars in its field of view.

When a star dims repeatedly and regularly, that is a good indication that a planet is passing between it and TESS.

By using the amount the light dims, and Doppler spectroscopy – that is, changes in the star’s light as it moves ever-so-slightly backwards and forwards due to the gravitational tug on the planet – astronomers can infer details about the planet, such as its size and mass.

 

Using this method, Kepler has discovered 2,652 confirmed planets to date between its first and second missions, located between 300 to 3,000 light-years away.

Kepler is still operational, but barely; it’s only a matter of time until it completely runs out of fuel.

TESS’s search is happening a lot closer, with targets between 30 and 300 light-years away – stars brighter than those observed by Kepler.

Thus, the exoplanets it identifies will be strong candidates to observe using spectroscopy, the analysis of light.

When a planet passes in front of a star, it has an effect on the light from the star, changing it based on the composition of its atmosphere (if it has one).

Ground-based observatories and the James Webb Space Telescope (once it launches in 2021) will have to make those follow-up observations.

Both papers are available on preprint resource arXiv. Pi Mensa c can be found here, and LHS 3844 b can be found here.

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Astronomers Just Found a Planet Where Star Trek’s Vulcan Was Predicted to Exist

So far, astronomers have identified thousands of exoplanets out there beyond the reaches of the Solar System, but only a rare few are the stuff of legend.

Such is the case with an Earth-like exoplanet, found orbiting a star called 40 Eridani A – Star Trek creator Gene Roddenberry’s preferred location for Vulcan, the home planet of Mr Spock.

Located around 16 light-years from Earth in the southern constellation of Eridanus, 40 Eridani A is part of a triple-star system.

Although it was never mentioned in the original TV series of Star Trek, it had been put forward as a proposed location for the planet by related literature.

In 1991, Roddenberry and three astronomers from the Harvard-Smithsonian Center for Astrophysics wrote a letter to Sky & Telescope magazine laying out their choice for Vulcan’s location, and why.

Based on the history of life on Earth, life on any planet around Epsilon Eridani would not have had time to evolve beyond the level of bacteria.




“On the other hand, an intelligent civilisation could have evolved over the aeons on a planet circling 40 Eridani. So the latter is the more likely Vulcan sun.

Epsilon Eridani does have one planet – an uninhabitable gas giant. Now astronomers on the University of Florida-led Dharma Planet Survey have found something that seems a bit more habitable orbiting 40 Eridani A.

More precisely, it’s an object known as a super-Earth – a rocky planet around twice the size of Earth, orbiting 40 Eridani A just inside the system’s habitable zone – not too hot and not too cold. It completes one orbit every 42 (Earth) days.

So life on the planet isn’t unfeasible.

The aim of the Dharma Planet Survey, using the 50-inch Dharma Endowment Foundation Telescope (DEFT) on Mount Lemmon in Arizona, is a dedicated survey to find low-mass planets orbiting bright, nearby stars.

It uses the radial velocity method – detecting the very slight wobble in a star’s position due to the gravitational pull of an exoplanet.

The candidate exoplanet, named HD 26965b (but we’ll probably call it Vulcan, obviously), is the first super-Earth found in the survey.

And if you’re in the southern hemisphere, you can even go outside and look for it.

“Now anyone can see 40 Eridani on a clear night and be proud to point out Spock’s home.”

The research has been published in the Monthly Notices of the Royal Astronomical Society.

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Atomic Iron And Titanium In The Atmosphere Of The Exoplanet KELT-9b

To constrain the formation history of an exoplanet, we need to know its chemical composition.

With an equilibrium temperature of about 4,050 kelvin, the exoplanet KELT-9b (also known as HD 195689b) is an archetype of the class of ultrahot Jupiters that straddle the transition between stars and gas-giant exoplanets and are therefore useful for studying atmospheric chemistry.

At these high temperatures, iron and several other transition metals are not sequestered in molecules or cloud particles and exist solely in their atomic forms




However, despite being the most abundant transition metal in nature, iron has not hitherto been detected directly in an exoplanet because it is highly refractory.

The high temperatures of KELT-9b imply that its atmosphere is a tightly constrained chemical system that is expected to be nearly in chemical equilibrium and cloud-free, and it has been predicted that spectral lines of iron should be detectable in the visible range of wavelengths.

Here we report observations of neutral and singly ionized atomic iron (Fe and Fe+) and singly ionized atomic titanium (Ti+) in the atmosphere of KELT-9b.

We identify these species using cross-correlation analysis of high-resolution spectra obtained as the exoplanet passed in front of its host star.

Similar detections of metals in other ultrahot Jupiters will provide constraints for planetary formation theories.

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NASA’s Planet-Hunting TESS Telescope Launches Today Aboard A SpaceX Rocket

Some of the most exciting space news of the past few years has been about Earth-like exoplanets that could one day (or perhaps already do) support life. TESS, a space telescope set to launch today aboard a SpaceX Falcon 9 rocket.

It will scan the sky for exoplanets faster and better than any existing platforms, expanding our knowledge of the universe and perhaps finding a friendly neighborhood to move to.

The Transit Exoplanet Survey Satellite has been in the works for years and in a way could be considered a sort of direct successor to the Kepler, the incredibly fruitful mission that has located thousands of exoplanets over nearly a decade.

But if Kepler was a telephoto aimed at dim targets far in the distance, TESS is an ultra-wide-angle lens that will watch nearly the entire visible sky.

They both work on the same principle, which is really quite simple: when a planet (or anything else) passes between us and a star (a “transit”), the brightness of that star temporarily dims.

By tracking how much dimmer and for how long over multiple transits, scientists can determine the size, speed, and other characteristics of the body that passed by.




It may seem like looking for a needle in a haystack, watching the sky hoping a planet will pass by at just the right moment.

But when you think about the sheer number of stars in the sky — and by the way, planets outnumber them — it’s not so crazy.

As evidence of this fact, in 2016 Kepler confirmed the presence of 1,284 new planets just in the tiny patch of sky it was looking at.

TESS will watch for the same thing with a much, much broader perspective.

Its camera array has four 16.4-megapixel imaging units, each covering a square of sky 24 degrees across, making for a tall “segment” of the sky like a long Tetris block.

The satellite will spend full 13.7-day orbits observing a segment, then move on to the next one.

There are 13 such segments in the sky’s Northern hemisphere and 13 in the southern; by the time TESS has focused on them all, it will have checked 85 percent of the visible sky.

It will be focusing on the brightest stars in our neighborhood: less than 300 light-years away and 30 to 100 times as bright as the ones Kepler was looking at.

The more light, the more data, and often the less noise — researchers will be able to tell more about stars that are observed, and if necessary dedicate other ground or space resources towards observing them.

Of course, with such close and continuous scrutiny of hundreds of thousands of stars, other interesting behaviors may be observed and passed on to the right mission or observatory.

Stars flaring or going supernova, bursts of interesting radiation, and other events could very well occur.

In fact, an overlapping area of observation above each of Earth’s poles will be seen for a whole year straight, increasing the likelihood of catching some rare phenomenon.

SpaceX is the launch partner, and the Falcon 9 rocket on which it will ride into orbit has already been test fired. TESS is packaged up and ready to go, as you see at right.

Currently the launch is planned for a 30-second window at 6:32 Florida time; if for some reason they miss that window, they’ll have to wait until the moon comes round again — a March 20 launch was already canceled.

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TRAPPIST-1 Planets Probably Rich In Water

Planets around the faint red star TRAPPIST-1, just 40 light-years from Earth, were first detected by the TRAPPIST-South telescope at ESO’s La Silla Observatory in 2016.

In the following year further observations from ground-based telescopes, including ESO’s Very Large Telescope and NASA’s Spitzer Space Telescope, revealed that there were no fewer than seven planets in the system, each roughly the same size as the Earth.

They are named TRAPPIST-1b,c,d,e,f,g and h, with increasing distance from the central star.

Further observations have now been made, both from telescopes on the ground, including the nearly-complete SPECULOOS facility at ESO’s Paranal Observatory, and from NASA’s Spitzer Space Telescope and the Kepler Space Telescope.

A team of scientists led by Simon Grimm at the University of Bern in Switzerland have now applied very complex computer modelling methods to all the available data and have determined the planets’ densities with much better precision than was possible before.




Simon Grimm explains how the masses are found: “The TRAPPIST-1 planets are so close together that they interfere with each other gravitationally, so the times when they pass in front of the star shift slightly.

“These shifts depend on the planets’ masses, their distances and other orbital parameters. With a computer model, we simulate the planets’ orbits until the calculated transits agree with the observed values, and hence derive the planetary masses.”

Team member Eric Agol comments on the significance: “A goal of exoplanet studies for some time has been to probe the composition of planets that are Earth-like in size and temperature.

“The discovery of TRAPPIST-1 and the capabilities of ESO’s facilities in Chile and the NASA Spitzer Space Telescope in orbit have made this possible — giving us our first glimpse of what Earth-sized exoplanets are made of!

The measurements of the densities, when combined with models of the planets’ compositions, strongly suggest that the seven TRAPPIST-1 planets are not barren rocky worlds.

They seem to contain significant amounts of volatile material, probably water, amounting to up to 5% the planet’s mass in some cases — a huge amount; by comparison the Earth has only about 0.02% water by mass!

TRAPPIST-1b and c, the innermost planets, are likely to have rocky cores and be surrounded by atmospheres much thicker than Earth’s.

TRAPPIST-1d, meanwhile, is the lightest of the planets at about 30 percent the mass of Earth. Scientists are uncertain whether it has a large atmosphere, an ocean or an ice layer.

Scientists were surprised that TRAPPIST-1e is the only planet in the system slightly denser than Earth, suggesting that it may have a denser iron core and that it does not necessarily have a thick atmosphere, ocean or ice layer.

It is mysterious that TRAPPIST-1e appears to be so much rockier in its composition than the rest of the planets.

In terms of size, density and the amount of radiation it receives from its star, this is the planet that is most similar to Earth.

TRAPPIST-1f, g and h are far enough from the host star that water could be frozen into ice across their surfaces.

If they have thin atmospheres, they would be unlikely to contain the heavy molecules that we find on Earth, such as carbon dioxide.

Astronomers are also working hard to search for further planets around faint red stars like TRAPPIST-1. As team member Michaël Gillon explains: “This result highlights the huge interest of exploring nearby ultracool dwarf stars — like TRAPPIST-1 — for transiting terrestrial planets.

“This is exactly the goal of SPECULOOS, our new exoplanet search that is about to start operations at ESO’s Paranal Observatory in Chile.

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