Here’s an artist’s depiction of the seven planets:

(NASA / JPL-Caltech)

The astronomers found the four newcomers by again measuring fluctuations in stellar light as the objects transited the parent star, revealing both their existence and information about their mass. Their findings suggest all seven are tidally locked, with one side perpetually facing TRAPPIST-1. (The habitable, water-friendly portion of each planet would likely be the ring between the hot, star-facing side and the cool, dark side.) The researchers estimate the orbital periods of the first six planets—the time they take to complete one loop around TRAPPIST-1—range between 1.5 and 12 days. The seventh planet made only one transit during the observations, so its orbit remains a mystery. The gravitational interactions between the six inner planets push them to orbit in a specific pattern around the star, a phenomenon known as a near-resonant chain. For example, for every eight orbits the innermost planet makes, the second makes exactly five. The system resembles Jupiter’s moons Ganymede, Europa, and Io, tidally locked objects that orbit in resonance, too.

TRAPPIST-1 and its septet of planets can’t be imaged directly, but that doesn’t matter much in the search for habitable planets. What’s needed is powerful telescopes capable of sweeping the system for biomarkers like oxygen and other exhalations of life. TRAPPIST-1 is a perfect target for star hunters like the James Webb Space Telescope, which in 2018 will begin scanning the skies from a vantage point of one million miles from Earth.

Until recently, red dwarfs were mostly overlooked in exoplanet exploration, but these ultracool stars seem to be proving skeptics wrong. Last August, astronomers using the European Southern Observatory in Chile discovered an Earth-sized planet orbiting in the temperate zone of Proxima Centauri, a red dwarf just four light-years away. In some ways their dimness is a boon for astronomers, as it makes it easier to see transiting objects and, potentially, signs of life on their surfaces. That’s good news, because red dwarfs are the most common kind of star in the Milky Way, accounting for more than three-fourths of the galaxy’s estimated 100 billion stars. There are likely many more systems like TRAPPIST-1, with plenty of Earth-sized planets.

The TRAPPIST-1 astronomers say they debated what a sunset may look on one of the tightly clustered planets. Despite its name, the red dwarf would emit a salmon hue, they decided, its darkest tones hidden in infrared, beyond the deepest red humans can see. The exoplanets could be frozen worlds, their icy crusts covered with cracks like the surface of Europa. Their terrain could carry the signs of water long gone, like channels carved by ancient floods on Mars. Or there could be water, lapping gently over rock beneath the salmon-colored sunset. And with luck, there might be something stirring underneath.</s>At least seven planets orbit this ultra cool dwarf star 40 light-years from Earth and they are all roughly the same size as the Earth. They are at the right distances from their star for liquid water to exist on the surfaces of several of them. This artist's impression is based on the known physical parameters for the planets and stars seen.

ESO / M. Kornmesser/spaceengine.org</s>Using NASA’s Spitzer Space Telescope, a team of astronomers has revealed the first known system of seven Earth-size planets around a single star. Three of these planets are firmly located in the habitable zone, the area around the parent star where a rocky planet is most likely to have liquid water.

The discovery sets a new record for greatest number of habitable-zone planets found around a single star outside our solar system. All of these seven planets could have liquid water – key to life as we know it – under the right atmospheric conditions, but the chances are highest with the three in the habitable zone.

“This discovery could be a significant piece in the puzzle of finding habitable environments, places that are conducive to life,” said Thomas Zurbuchen, associate administrator of the agency’s Science Mission Directorate in Washington. “Answering the question ‘are we alone’ is a top science priority and finding so many planets like these for the first time in the habitable zone is a remarkable step forward toward that goal.”



 Seven Earth-sized planets have been observed by NASA’s Spitzer Space Telescope around a tiny, nearby, ultra-cool dwarf star called TRAPPIST-1. Three of these planets are firmly in the habitable zone.

At about 40 light-years (235 trillion miles) from Earth, the system of planets is relatively close to us, in the constellation Aquarius. Because they are located outside of our solar system, these planets are scientifically known as exoplanets.

This exoplanet system is called TRAPPIST-1, named for The Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile. In May 2016, researchers using TRAPPIST announced they had discovered three planets in the system. Assisted by several ground-based telescopes, including the European Southern Observatory’s Very Large Telescope, Spitzer confirmed the existence of two of these planets and discovered five additional ones, increasing the number of known planets in the system to seven.

The new results were published Wednesday in the journal Nature, and announced at a news briefing at NASA Headquarters in Washington.

Using Spitzer data, the team precisely measured the sizes of the seven planets and developed first estimates of the masses of six of them, allowing their density to be estimated.

Based on their densities, all of the TRAPPIST-1 planets are likely to be rocky. Further observations will not only help determine whether they are rich in water, but also possibly reveal whether any could have liquid water on their surfaces. The mass of the seventh and farthest exoplanet has not yet been estimated – scientists believe it could be an icy, “snowball-like” world, but further observations are needed.

“The seven wonders of TRAPPIST-1 are the first Earth-size planets that have been found orbiting this kind of star,” said Michael Gillon, lead author of the paper and the principal investigator of the TRAPPIST exoplanet survey at the University of Liege, Belgium. “It is also the best target yet for studying the atmospheres of potentially habitable, Earth-size worlds.”

In contrast to our sun, the TRAPPIST-1 star – classified as an ultra-cool dwarf – is so cool that liquid water could survive on planets orbiting very close to it, closer than is possible on planets in our solar system. All seven of the TRAPPIST-1 planetary orbits are closer to their host star than Mercury is to our sun. The planets also are very close to each other. If a person was standing on one of the planet’s surface, they could gaze up and potentially see geological features or clouds of neighboring worlds, which would sometimes appear larger than the moon in Earth’s sky.

The planets may also be tidally locked to their star, which means the same side of the planet is always facing the star, therefore each side is either perpetual day or night. This could mean they have weather patterns totally unlike those on Earth, such as strong winds blowing from the day side to the night side, and extreme temperature changes.

Spitzer, an infrared telescope that trails Earth as it orbits the sun, was well-suited for studying TRAPPIST-1 because the star glows brightest in infrared light, whose wavelengths are longer than the eye can see. In the fall of 2016, Spitzer observed TRAPPIST-1 nearly continuously for 500 hours. Spitzer is uniquely positioned in its orbit to observe enough crossing – transits – of the planets in front of the host star to reveal the complex architecture of the system. Engineers optimized Spitzer’s ability to observe transiting planets during Spitzer’s “warm mission,” which began after the spacecraft’s coolant ran out as planned after the first five years of operations.

“This is the most exciting result I have seen in the 14 years of Spitzer operations,” said Sean Carey, manager of NASA’s Spitzer Science Center at Caltech/IPAC in Pasadena, California. “Spitzer will follow up in the fall to further refine our understanding of these planets so that the James Webb Space Telescope can follow up. More observations of the system are sure to reveal more secrets.”

Following up on the Spitzer discovery, NASA’s Hubble Space Telescope has initiated the screening of four of the planets, including the three inside the habitable zone. These observations aim at assessing the presence of puffy, hydrogen-dominated atmospheres, typical for gaseous worlds like Neptune, around these planets.



 This 360-degree panorama depicts the surface of a newly detected planet, TRAPPIST 1-d, part of a seven planet system some 40 light years away. Explore this artist’s rendering of an alien world by moving the view using your mouse or your mobile device.

In May 2016, the Hubble team observed the two innermost planets, and found no evidence for such puffy atmospheres. This strengthened the case that the planets closest to the star are rocky in nature.

“The TRAPPIST-1 system provides one of the best opportunities in the next decade to study the atmospheres around Earth-size planets,” said Nikole Lewis, co-leader of the Hubble study and astronomer at the Space Telescope Science Institute in Baltimore, Maryland. NASA’s planet-hunting Kepler space telescope also is studying the TRAPPIST-1 system, making measurements of the star’s minuscule changes in brightness due to transiting planets. Operating as the K2 mission, the spacecraft’s observations will allow astronomers to refine the properties of the known planets, as well as search for additional planets in the system. The K2 observations conclude in early March and will be made available on the public archive.

Spitzer, Hubble, and Kepler will help astronomers plan for follow-up studies using NASA’s upcoming James Webb Space Telescope, launching in 2018. With much greater sensitivity, Webb will be able to detect the chemical fingerprints of water, methane, oxygen, ozone, and other components of a planet’s atmosphere. Webb also will analyze planets’ temperatures and surface pressures – key factors in assessing their habitability.

Publication: Michaël Gillon, et al., “Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1,” Nature 542, 456–460 (23 February 2017) doi:10.1038/nature21360</s>There have been many discoveries of potentially habitable planets orbiting stars other than our own over the last few years.

Now things are getting even more exciting. Scientists have documented a star surrounded by no fewer than seven Earth-like planets – several or all of which could be at the right temperature for liquid water, and potentially life, to exist.

But is it possible to know anything about what these planets are like beyond simple measures such as temperature and mass? There are indeed several factors that can give us a clue. So let’s take a look at what planetary processes we might expect to find there – and ultimately whether life could exist.

The seven planets orbit an “ultracool dwarf” about 39 light years away. But don’t think this star is wearing shades. With a mass of only 8% of the sun’s and shining less than 0.1% as brightly, it is at the small, faint end of the “red dwarf” star type, barely able to power itself by nuclear fusion. Proxima, the nearest star beyond the solar system (4.24 light years away), where recently a single planet was discovered, has 12% of the sun’s mass and is an ordinary (not ultracool) red dwarf.

In 2010, a group of scientists began monitoring the closest dwarf stars using a robotic telescope in Chile called TRAPPIST (the Transiting Planets and Planetesimals Small Telescope). They were hoping to find periodic dips in brightness caused by a planet passing in front of the star’s disc, cutting out part of its light (a transit). In 2016, they found their first candidate: an ultracool dwarf.

They named this star TRAPPIST-1 and began to study it with more powerful telescopes, including NASA’s Spitzer space telescope. This fuller survey has now revealed a total of seven transiting exoplanets there (see video).

The amount of light blocked out by each exoplanet during a transit reveals its size. The repeat frequency reveals each exoplanet’s orbital period, from which the laws of gravity allow us to deduce its distance from the star. These exoplanets have no names, but by convention are designated as TRAPPIST-1b (the innermost) to TRAPPIST-1h (the outermost).

Amazingly, the planets of TRAPPIST-1 span only a narrow range of sizes, not much different to Earth. They huddle round their star almost as closely as Jupiter’s major moons to Jupiter, and are all much closer to their star than the Earth is to the sun. However, TRAPPIST-1 is so faint that even its innermost planet may be just about cool enough for liquid water to exist on its surface, while its outermost planet may be just warm enough to avoid global freezing.

Transits reveal exoplanets’ sizes rather than their masses, but mass can be deduced when, as in the TRAPPIST-1 system, there are slight irregularities in transit timings attributable to neighbouring exoplanets perturbing each others’ orbits. This suggests that most of the family are Earth-like in their density and not just their size. There is no way to be sure yet how much water most of them have, if any. Similarly, it’s hard to know whether any resemblance to Earth extends as far as having plate tectonics and a distinction between oceanic and continental crust (like Earth) or a more globally homogeneous crust (like Mars and Venus).

The exception is TRAPPIST-1f which seems to be notably less dense, implying a lot more water and less rock and iron. If this planet has a deep global ocean we can imagine it as one with many hot springs or even volcanoes on its floor. This is because the planets b through g have “resonant orbits” (their periods are simple multiples of each other) leading to a tidal pull that distorts their interiors and adds heat in addition to the heat generated internally by decay of radioactive elements contained within the rock.

With most or maybe even all of its seven known planets in the not-too-hot, not-too-cold “Goldilocks zone” around the star, TRAPPIST-1 offers the intriguing prospect of several Earth-like planets capable of hosting Earth-like life around the same star.

TRAPPIST-1 is young as ultracool dwarfs go, maybe only half a billion years old. But thanks to the frugal rate at which it uses its nuclear fuel it has a further 10 trillion years left to run (a thousand times longer then the sun). On Earth, it took two billion years to go from microbes to multi-cellular organisms, and another billion years for intelligence to emerge. So while we may not expect advanced civilisations to exist on the TRAPPIST-1 planets, some simple lifeforms may be in the works or already exist.

We don’t yet know how easy it is for life to get started even when conditions are right. But were life to exist or suddenly begin on any of TRAPPIST-1’s planets it is very likely that it would spread to its neighbours, as shown in a recent study.

Dwarf stars are more common than sun-like stars, and now we know they can have numerous Earth-like planets. It is beginning to look as if stars like our sun, a fast-burning “main sequence star”, may be less important as hosts for life-bearing planets than their stunted cousins.

TRAPPIST-1 and its planets are sure to be among the prime targets for the James Webb Space Telescope, likely to begin operations in 2019. This should be able to detect the presence of any atmosphere about a planet while it is in transit across the star and maybe even reveal whether atmospheric composition seems to have been modified by living processes.

A version of this article originally appeared on the conversation.com</s>WASHINGTON — Astronomers have found at least seven Earth-like planets orbiting the same star 40 light-years away, according to a study published Wednesday in the journal Nature. The findings were also announced at a news conference at NASA Headquarters in Washington.

This discovery outside of our solar system is rare because the planets have the winning combination of being similar in size to Earth and being all temperate, meaning they could have water on their surfaces and potentially support life.

“This is the first time that so many planets of this kind are found around the same star,” said Michaël Gillon, lead study author and astronomer at the University of Liège in Belgium.

The seven exoplanets were all found in tight formation around an ultracool dwarf star called TRAPPIST-1. Estimates of their mass also indicate that they are rocky planets, rather than being gaseous like Jupiter. Three planets are in the habitable zone of the star, known as TRAPPIST-1e, f and g, and may even have oceans on the surface.

The researchers believe that TRAPPIST-1f in particular is the best candidate for supporting life. It’s a bit cooler than Earth, but could be suitable with the right atmosphere and enough greenhouse gases.

If TRAPPIST-1 sounds familiar, that’s because these researchers announced the discovery of three initial planets orbiting the same star in May. The new research increased that number to seven planets total.

“I think we’ve made a crucial step towards finding if there is life out there,” said Amaury Triaud, one of the study authors and an astronomer at the University of Cambridge. “I don’t think any time before we had the right planets to discover and find out if there was (life). Here, if life managed to thrive and releases gases similar to what we have on Earth, we will know.”

Life may begin and evolve differently on other planets, so finding the gases that indicate life is key, the researchers added.

What we know

The planets are so close to each other and the star that there are seven of them within a space five times smaller than the distance from Mercury to our sun. This proximity allows the researchers to study the planets in depth as well, gaining insight about planetary systems other than our own.

Starting closest to the star and moving out, the planets have respective orbits from one and a half to nearly 13 Earth days. The orbit of the farthest planet is still unknown.

Standing on the surface of one of the planets, you would receive 200 times less light than you get from the sun, but you would still receive just as much energy to keep you warm since the star is so close. It would also afford some picturesque views, as the other planets would appear in the sky as big as the moon (or even twice as big).

On TRAPPIST-1f, the star would appear three times as big as the sun in our sky. And because of the red nature of the star, the light would be a salmon hue, the researchers speculate.

Based on preliminary climate modeling, the researchers believe that the three planets closest to the star may be too warm to support liquid water, while the outermost planet, TRAPPIST-1h, is probably too distant and cold to support water on the surface. But further observation is needed to know for sure.

How the discovery was made

TRAPPIST-1 barely classifies as a star at half the temperature and a tenth the mass of the sun. It is red, dim and just a bit larger than Jupiter. But these tiny ultracool dwarf stars are common in our galaxy.

They were largely overlooked until Gillon decided to study the space around one of these dwarves.

The researchers used a telescope called TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) to observe its starlight and changes in brightness. The team saw shadows, like little eclipses, periodically interrupting the steady pattern of starlight. This is called transiting. The shadows indicated planets, and further observation confirmed them.

In July, the team was able to determine that two of the closest planets to the stars had atmospheres that were more compact and comparable to those of Earth, Venus and Mars by observing starlight through the planets’ atmosphere.

By using a global network ground-based telescopes like TRAPPIST and space-based telescopes like Spitzer, the researchers continued looking toward the TRAPPIST system and were able to determine the orbital periods, distances from their star, radius and and masses of the planets.

Over the next decade, the researchers want to define the atmosphere of each planet, as well as to determine whether they truly do have liquid water on the surface and search for signs of life.

Although 40 light-years away doesn’t sound too far, it would take us millions of years to reach this star system. But from a research perspective, it’s a close opportunity and the best target to search for life beyond our solar system.

“If we learn something now, it can determine if we looked in the right place,” Gillon said.

In 2018, the James Webb Space Telescope will launch and be positioned 1 million miles from Earth with an unprecedented view of the universe. It can observe large exoplanets and detect starlight filtered through their atmosphere.

The researchers are also searching for similar star systems to conduct more atmospheric research. Four telescopes named SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) based in Chile will survey the southern sky for this purpose.

This star system will probably outlive us because this type of star evolves so slowly. When our sun dies, TRAPPIST-1 will still be a young star and will live for another trillion years, Gillon said. After we are gone, if there is another part of the universe for life to carry on, it may be in the TRAPPIST-1 system.</s>This artist's concept shows what each of the TRAPPIST-1 planets may look like, based on available data about their sizes, masses and orbital distances. (NASA/JPL-Caltech)

Forthy light-years from Earth, scientists have discovered seven "Earth-sized planets" in the largest-ever cache of planets found around a single star outside of our solar system.

"The discovery gives us a hint that finding a second Earth is not just a matter of if, but when," said Thomas Zurbuchen, associate administrator of the Science Mission Directorate at NASA Headquarters. "You can just imagine how many worlds are out there that have a shot at becoming a habitable ecosystem that we can explore."

Three of the newly discovered planets are in what's known as the habitable zone, the area around a star where a rocky planet is most likely to have liquid water, according to NASA. The Hubble Space Telescope has started to scan four of the planets, including the three found in the habitable zone.

The planets were found by astronomers using ground and space telescopes around an ultracool, red dwarf star named TRAPPIST-1, according to the European Organisation for Astronomical Research in the Southern Hemisphere (ESO).

The findings were published Wednesday in the scientific journal Nature. The paper's lead author, astronomer Michael Gillon, described the planets as "the seven wonders of TRAPPIST-1."

"The energy output from dwarf stars like TRAPPIST-1 is much weaker than that of our sun," said Amaury Triaud, one of the co-authors of the Nature paper. "Planets would need to be in far closer orbits than we see in the solar system if there is to be surface water. Fortunately, it seems that this kind of compact configuration is just what we see around TRAPPIST-1."

Scientists characterized the discovery as a significant leap in the search for alien life during a news conference on Wednesday afternoon.

"Answering the question, 'Are we alone?' is a top science priority, and finding so many planets like these for the first time in the habitable zone is a remarkable step forward toward that goal," Zurbuchen said.

The planets were spotted when scientists noticed dips in TRAPPIST-1's light output, according to ESO. The discovery was made using Spitzer, an infrared telescope that trails Earth as it orbits the sun, NASA officials said.

Astronomers determined that the dips were caused by the planets as they passed between the star and Spitzer.

The planets have been temporarily named with letters, TRAPPIST-1b through TRAPPIST-1h, in order of increasing distance from their parent star.</s>WASHINGTON (WHTM) – NASA says it’s found seven Earth-sized planets outside of our solar system that could hold life as we know it.

Researchers said the seven worlds are around a single sun, an ultra-cool dwarf star called TRAPPIST-1, and all have the potential for water on their surface.

Three of the planets are firmly located in the habitable zone, the area around a sun where a planet is most likely to have liquid water under the right atmospheric conditions.

The discovery sets a new record for greatest number of habitable-zone planets found around a single star outside our solar system.

The system of planets is relatively close to us, about 40 light-years, in the constellation Aquarius. Planets located outside of our solar system are scientifically known as exoplanets.

NASA said the planets are likely to be rocky, but the seventh and farthest exoplanet could be an icy, “snowball-like” world.

The planets may also be tidally locked to their sun, which means the same side of the planet is always facing the star. This could mean they have weather patterns totally unlike those on Earth, such as strong winds and extreme temperature changes.

The discovery was made using NASA’s Spitzer Space Telescope, an infrared telescope that trails Earth as it orbits the sun.

The finding was published Wednesday in the journal Nature and announced at a news briefing at NASA Headquarters in Washington.

Get breaking news, weather and traffic on the go. Download our News App and our Weather App for your phone and tablet.</s>Finding a 'second Earth' may be just a matter of 'when' rather than 'if', suggest astronomers who discovered a new solar system of seven planets with the potential to host life located less than 40 light years away.

 

 The US space agency's Space Telescope found the first known system of seven Earth-sized planets around a single star.

Three of these planets are located in the habitable zone, the area around the parent star where a rocky planet is most likely to have liquid water.The discovery sets a new record for greatest number of habitable-zone planets found around a single star outside our solar system.All of the seven planets could have liquid water - key to life as we know it - under right atmospheric conditions, but the chances are highest with the three in the habitable zone."This discovery could be a significant piece in the puzzle of finding habitable environments, places that are conducive to life," said Thomas Zurbuchen, associate administrator at NASA's Science Mission Directorate in Washington."Answering the question 'are we alone' is a top science priority and finding so many planets like these for the first time in the habitable zone is a remarkable step forward toward that goal," said Zurbuchen.At about 40 light-years - 235 trillion miles - from Earth, the system of planets is relatively close to us, in the constellation Aquarius.The exoplanet system is called TRAPPIST-1, named for The Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile.In May 2016, researchers using TRAPPIST announced they had discovered three planets in the system.Assisted by several ground-based telescopes, including the European Southern Observatory's Very Large Telescope, confirmed the existence of two of these planets and discovered five additional ones, increasing the number of known planets in the system to seven.Following up on the discovery, NASA's Hubble Space Telescope has initiated the screening of four of the planets, including the three inside the habitable zone.These observations aim at assessing the presence of puffy, hydrogen-dominated atmospheres, typical for gaseous worlds like Neptune, around these planets.The findings were published in the journal Nature.</s>NASA official says discovery gives hint that finding a second Earth is 'just a matter' of time.

A group of international scientists have announced that a dwarf star just 40 light years from the Earth has at least seven apparently rocky planets with potential to harbour water and life.

The discovery of the planets, which are all about the size of Earth or smaller, was announced at the NASA headquarters in Washington, DC, and published in the journal Nature on Wednesday.

"Looking for life elsewhere, this system is probably our best bet as of today," said Brice-Olivier Demory, professor at the University of Bern's Centre for Space and Habitability and one of the authors of a paper on the planets around TRAPPIST-1, a small, ultracool star.

Inside Story: Is travel to Mars on the horizon?

The TRAPPIST-1's planets are similar to the inner solar system around Earth's sun, Demory's analysis of data from NASA's Spitzer Space Telescope showed.

The discovery sets a new record for greatest number of habitable-zone planets found around a single star outside our solar system, NASA said.

Like previous exoplanets - or planets beyond Earth's solar system - TRAPPIST-1's satellites were spotted when astronomers saw the planets "transit" the star, blocking some of the light captured by telescopes.

"The discovery gives us a hint that finding a second Earth is not just a matter of if, but when," said Thomas Zurbuchen, of the Science Mission Directorate at NASA.

"This discovery could be a significant piece in the puzzle of finding habitable environments, places that are conducive to life," Zurbuchen added.

"Answering the question 'are we alone' is a top science priority, and finding so many planets like these for the first time in the habitable zone is a remarkable step forward toward that goal."

All seven planets are in orbits even closer than Mercury, the Sun's nearest planet, causing frequent transits and plentiful opportunities for observation and collection of data.

But because TRAPPIST-1 is so small and cool - about one-tenth the size and half the temperature of the sun - at least three of the planets could be cool enough for water and, possibly, life, despite their tight orbits.

They fall clearly within the so-called habitable zone. 

 

Further data used in the Nature paper was collected from several ground telescopes around the world.

Demory said that future telescopes, including the James Webb Space Telescope, which is to succeed the orbiting Hubble Space Telescope, "will have the possibility to detect the signature of ozone if this molecule is present in the atmosphere of one of these planets".

He said that ozone "could be an indicator for biological activity on the planet", but cautioned that signs of life are difficult to assert from interstellar distances.</s>In what is surely the biggest news since the hunt for exoplanets began, NASA announced today the discovery of a system of seven exoplanets orbiting the nearby star of TRAPPIST-1. Discovered by a team of astronomers using data from the TRAPPIST telescope in Chile and the Spitzer Space Telescope, this find is especially exciting since all of these planets are believed to be Earth-sized and terrestrial (i.e. rocky).

But most exciting of all is the fact that three of these rocky exoplanets orbit within the star’s habitable zone (aka. “Goldilocks Zone”). This means, in effect, that these planets are capable of having liquid water on their surfaces and could therefore support life. As far as extra-solar planet discoveries go, this is without precedent, and the discovery heralds a new age in the search for life beyond our Solar System.

The team behind the discovery was led by Michael Gillon, an astronomer from the University of Liege in Belgium. Using the The Transiting Planets and Planetesimals Small Telescope (TRAPPIST) telescope at the European Southern Observatory’s (ESO) La Silla Observatory in Chile, he and his colleagues first noticed the presence of two planets in the TRAPPIST-1 system in May of 2016.

The team made their observations of this star system – which is located about 39 light years from Earth in the direction of the Aquarius constellation – from September to December 2015. This discovery was immediately followed-up using several ground-based telescopes, which included including the ESO’s Very Large Telescope, and the Spitzer Space Telescope.

Data from these surveys confirmed the existence of the two planets, and revealed five more – making this the largest find around a single star in exoplanet-hunting history. Relying on the Spitzer data, Dr. Gillon and his team were also able to obtain precise information on the planets using the transit method. By measuring the periodic dips in TRAPPIST-1’s luminosity (from the planet’s passing in front of it), they were able to measure their sizes, masses and densities.

This is especially important when studying exoplanets. Not only does it allow scientists to make accurate assessments of a planet’s composition (i.e. whether or not its rocky, icy, or gaseous), it is key in determining whether or not a planet could be habitable. It was also the first time in which accurate constraints were placed upon the masses and radii of exoplanets using this method.

A follow-up survey was then mounted with NASA’s Hubble Space Telescope to study the three innermost planets and look for signs of hydrogen and helium – the chemical signatures that would indicate if the planets were gas giants. Hubble detected no evidence of hydrogen and helium atmospheres, which only strengthened the case for these planets being rocky in nature.

Another exciting aspect of all this is that these seven exoplanets – which are some of the best candidates for habitability – are near enough to Earth to be studies closely. As Michael Gillon, lead author of the paper and the principal investigator of the TRAPPIST exoplanet survey at the University of Liege, said in a NASA press release:

Nikole Lewis, the co-leader of the Hubble study and an astronomer at the Space Telescope Science Institute, was also on hand at the NASA press briefing where the findings were announced. There, she shared information that was obtained by the Hubble Space Telescope. And as she explained, of the three worlds that are in the habitable zone – TRAPPIST-1e, f, and g – all experience conditions that are very similar to what we experience here on Earth.

TRAPPIST-1e is the innermost of the three exoplanets. It is very close in size to Earth, and receives about the same amount of light as Earth does – which means temperatures are likely to be very close to Earth’s as well. TRAPPIST-1f, meanwhile, is a potentially-water rich world that is also likely to be the same size as Earth. It has a 9-day orbit, and receives about the same amount of sunlight as Mars.

The outermost of the habitable zone planets is Trappist 1g. With a radius that is 13% larger than that of Earth, it is the largest planet in the system, and receives about the same amount of light as a body positioned between Mars and the Asteroid Belt would. Between these three exoplanets, and the four others in the system, astronomers now have a multiple candidates within the same star system to study what potentially-habitable worlds might look like.

During the course of the NASA press briefing, Dr. Gillon stressed why the discovery of this system is a major boon for astronomers and planetary scientists. Not only is this the first time that so many exoplanets have been discovered around the same star, but the fact that it is a red dwarf – a class of small, cooler, dimmer stars – is especially encouraging.

Compared to other classes, red dwarfs (aka. M-class stars) are the most frequent type of star in the Universe – making up an estimated 70% of stars in our galaxy alone. On top of that, the TRAPPIST-1 system is rather unique. As Gillon explained, the planets are in close enough proximity that they gravitationally interact with one another. Their proximity would also make for some excellent viewing opportunities for a person standing on the surface of one of them.

“The planets are close enough to each other,” he said, “that if you were on the surface of one, you would have a wonderful view of the others. You would see them not as we see Venus or Mars from Earth (as bright stars), but as we see the Moon. They would be as large or larger than the Moon.”

In the coming weeks and months, NASA plans to follow-up on this system of planets even more. At the moment, the Kepler space telescope is studying the system, conducting measurements of minuscule changes in the star’s brightness due to transiting planets. Operating as the K2 mission, the spacecraft’s observations will allow astronomers to refine the properties of the known planets, as well as search for additional planets in the system.

In the meantime, Dr. Gillon and his team will be using ground-based telescopes to search 1000 of the nearest ultra-cool dwarf stars to see if they too have multi-planet systems. Nikole Lewis indicated that Hubble will be conducting further observations of TRAPPIST-1 in order to obtain information about the planets’ atmospheres.

These studies will determine what gases make up the atmospheres, but will also be looking for tell-tale signs of those that indicate the presence of organic life – i.e. methane, ozone, oxygen, etc.

“The TRAPPIST-1 system provides one of the best opportunities in the next decade to study the atmospheres around Earth-size planets,” she said. “Not only will these studies let us know if any of these planets have the kind of atmospheres that are conducive to life, they will also tell us much about the formation and evolution processes of the surface – which are also key factors in determining habitability.”

The Spitzer Space Telescope will also be trained on this system in order to obtain follow-up information on the planets’ atmospheres. Besides looking for biological indicators (such as oxygen gas, ozone and methane), it will also be trying to determine the greenhouse gas content of the atmospheres – which will help put further constrains on the surface temperatures of the planets.

On top of that, next-generation missions – like the James Webb Telescope – are expected to play a vital role in learning more about this system. As Sara Seager – a professor of planetary science and physics at MIT – explained in the course of the briefing, the discovery of a system with multiple potentially-habitable planets was a giant, accelerated leap forward in the hunt for life beyond our Solar System.

“Goldilocks has several sisters,” as she put it. “An amazing system like this one lets us know there are many more life-bearing worlds out there. This star system is a veritable laboratory for studying stars orbiting very cool, very dim stars. We get to test many theories about these worlds, being tidally-locked and amount of radiation coming from host star.”

Thomas Zurbuchen – the associate administrator of NASA’s Science Mission Directorate – was also on hand at the briefing. In addition to expressing how this was a first for NASA and exoplanet-hunters everywhere, he also expressed how exciting it was in the context of searching for life beyond our Solar System:

By Matt Williams - 

 Matt Williams is the Curator of the Guide to Space for Universe Today, a regular contributor to HeroX, a science fiction author, and a Taekwon-Do instructor. He lives with his family on Vancouver Island in beautiful BC.
NASA and the European Southern Observatory announce the discovery of four new Earth-like planets in the Goldilocks zone of the star TRAPPIST-1, in addition to the three discovered there last year.