Starship Asterisk*

Comparison of the TRAPPIST-1 system with the inner Solar System and the Galilean Moons of Jupiter -- Credit: ESO/O. Furtak

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Comparison of the sizes of the TRAPPIST-1 planets with Solar System bodies -- Credit: ESO/O. Furtak

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Astronomers have found a system of seven Earth-sized planets just 40 light-years away. Using ground and space telescopes, including ESO’s Very Large Telescope, the planets were all detected as they passed in front of their parent star, the ultracool dwarf star known as TRAPPIST-1. According to the paper appearing today in the journal Nature, three of the planets lie in the habitable zone and could harbour oceans of water on their surfaces, increasing the possibility that the star system could play host to life. This system has both the largest number of Earth-sized planets yet found and the largest number of worlds that could support liquid water on their surfaces.

Astronomers using the TRAPPIST–South telescope at ESO’s La Silla Observatory, the Very Large Telescope (VLT) at Paranal and the NASA Spitzer Space Telescope, as well as other telescopes around the world [1], have now confirmed the existence of at least seven small planets orbiting the cool red dwarf star TRAPPIST-1 [2]. All the planets, labelled TRAPPIST-1b, c, d, e, f, g and h in order of increasing distance from their parent star, have sizes similar to Earth [3].

Dips in the star’s light output caused by each of the seven planets passing in front of it — events known as transits — allowed the astronomers to infer information about their sizes, compositions and orbits [4]. They found that at least the inner six planets are comparable in both size and temperature to the Earth. ...

With just 8% the mass of the Sun, TRAPPIST-1 is very small in stellar terms — only marginally bigger than the planet Jupiter — and though nearby in the constellation Aquarius (The Water Carrier), it appears very dim. Astronomers expected that such dwarf stars might host many Earth-sized planets in tight orbits, making them promising targets in the hunt for extraterrestrial life, but TRAPPIST-1 is the first such system to be found. ...

The team determined that all the planets in the system are similar in size to Earth and Venus in the Solar System, or slightly smaller. The density measurements suggest that at least the innermost six are probably rocky in composition.

The planetary orbits are not much larger than that of Jupiter’s Galilean moon system, and much smaller than the orbit of Mercury in the Solar System. However, TRAPPIST-1’s small size and low temperature mean that the energy input to its planets is similar to that received by the inner planets in our Solar System; TRAPPIST-1c, d and f receive similar amounts of energy to Venus, Earth and Mars, respectively.

All seven planets discovered in the system could potentially have liquid water on their surfaces, though their orbital distances make some of them more likely candidates than others. Climate models suggest the innermost planets, TRAPPIST-1b, c and d, are probably too hot to support liquid water, except maybe on a small fraction of their surfaces. The orbital distance of the system’s outermost planet, TRAPPIST-1h, is unconfirmed, though it is likely to be too distant and cold to harbour liquid water — assuming no alternative heating processes are occurring [5]. TRAPPIST-1e, f, and g, however, represent the holy grail for planet-hunting astronomers, as they orbit in the star’s habitable zone and could host oceans of surface water [6]. ...

Imagine standing on the surface of the exoplanet TRAPPIST-1f. This artist's concept is one interpretation of what it could look like Credit: NASA/JPL-Caltech

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Imagine standing on the surface of the exoplanet TRAPPIST-1f. This artist's concept is one interpretation of what it could look like Credit: NASA/JPL-Caltech

NASA's Spitzer Space Telescope 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. ...

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. ...

• Nature 542(7642):456 (23 Feb 2017) DOI: 10.1038/nature21360 (preprint)

This video details a system of seven planets orbiting TRAPPIST-1, a discovery of the Spitzer Space Telescope, operated by NASA's Jet Propulsion Laboratory in Pasadena, California. TRAPPIST-1 is an ultra-cool dwarf star. Over 21 days, Spitzer measured the drop in light as each planet passed in front of the star. Spitzer was able to identify a total of seven rocky worlds, including three in the habitable zone where life is possible. The study established the planets' size, distance from their sun and, for some of them, their approximate mass and density. It also established that some, if not all, these planets are tidally locked, meaning one face of the planet permanently faces their sun.

• orbits are all set up such that:
  
  each outer/inner planet is
  near aphelion/perihelion

neufer wrote:

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I noticed all the planets seem to be in a 3:2 resonance
with their neighboring planets a la Pluto/Neptune.

Does that mean that their elliptical

• orbits are all set up such that:
  
  each outer/inner planet is
  near aphelion/perihelion

at inferior conjunction.

Doum wrote:trappist-1 is around 500 million years old. Life on earth did appear when it was 500 million years old. So, using earth as reference because its all we know, there might be very primitive lifeform overthere. Of course life might be more evolve then that. Natural occuring and evolution of life might be different then here on eath. i wouldnt expect detection of a signal coming from there. But who knows? It is still fascinating. WOW!

Wikipedia wrote:
TRAPPIST-1 is an ultracool dwarf star that is approximately 8% the mass of and 11% the radius of the Sun. It has a temperature of 2550 K and is at least 500 million years old[4], though it could theoretically be billions, or even hundreds of billions[17], of years old.

BDanielMayfield wrote:
Trappist-1 is only about 39 light years away, it has just barely enough mass to even be a normal star (which means it will shine on for 10 Trillion years) and its family of 7 planets (so far) all orbit at an almost perfect 90 degrees to our line of sight! What are the odds? No really, I wonder what the odds of all these factors converging really are, and what this says about the vast numbers of planets that must exist!

• About 0.8% for the most distant of the planets.

neufer wrote:

BDanielMayfield wrote:
Trappist-1 is only about 39 light years away, it has just barely enough mass to even be a normal star (which means it will shine on for 10 Trillion years) and its family of 7 planets (so far) all orbit at an almost perfect 90 degrees to our line of sight! What are the odds? No really, I wonder what the odds of all these factors converging really are, and what this says about the vast numbers of planets that must exist!

• About 0.8% for the most distant of the planets.

Ann wrote:I must agree that the TRAPPIST-1 system is amazing. Imagine a star only 8% the mass of the Sun whose accretion disk also produced no fewer than seven planets that are comparable to the Earth in size and mass!

I read somewhere that metal-poor stars have been born out of nebulas that were able to produce rocky planets like the Earth, but no or few gas giants. The TRAPPIST-1 metal-rich nebula produced no fewer than seven "Earths", but not a single Jupiter or Neptune! ...

BDanielMayfield wrote:

Ann wrote:I must agree that the TRAPPIST-1 system is amazing. Imagine a star only 8% the mass of the Sun whose accretion disk also produced no fewer than seven planets that are comparable to the Earth in size and mass!

I read somewhere that metal-poor stars have been born out of nebulas that were able to produce rocky planets like the Earth, but no or few gas giants. The TRAPPIST-1 metal-rich nebula produced no fewer than seven "Earths", but not a single Jupiter or Neptune! ...

The nebula TRAPPIST-1 and company formed from was metal rich? Where'd ya hear that? Wikipedia lists the star's metallicity at just 0.04+/-0.08 dex. Very Sunlike.

Wikipedia wrote:
The star is metal-rich, with a metallicity ([Fe/H]) of 0.04, or 109% the solar amount. This is particularly odd as such low-mass stars near the boundary between brown dwarfs and hydrogen-fusing stars are expected to have considerably less metallic composition than the Sun.

Ann wrote:

Doum wrote:trappist-1 is around 500 million years old. Life on earth did appear when it was 500 million years old. So, using earth as reference because its all we know, there might be very primitive lifeform overthere. Of course life might be more evolve then that. Natural occuring and evolution of life might be different then here on eath. i wouldnt expect detection of a signal coming from there. But who knows? It is still fascinating. WOW!

Wikipedia wrote:
TRAPPIST-1 is an ultracool dwarf star that is approximately 8% the mass of and 11% the radius of the Sun. It has a temperature of 2550 K and is at least 500 million years old[4], though it could theoretically be billions, or even hundreds of billions[17], of years old.

TRAPPIST-1 is at least 500 million years old, and it could be much older.

TRAPPIST-1 is somewhat similar to Proxima Centauri when it comes to mass and luminosity, although it is even fainter and smaller than Proxima.

Ann

Ann wrote:

BDanielMayfield wrote:

Ann wrote:I must agree that the TRAPPIST-1 system is amazing. Imagine a star only 8% the mass of the Sun whose accretion disk also produced no fewer than seven planets that are comparable to the Earth in size and mass!

I read somewhere that metal-poor stars have been born out of nebulas that were able to produce rocky planets like the Earth, but no or few gas giants. The TRAPPIST-1 metal-rich nebula produced no fewer than seven "Earths", but not a single Jupiter or Neptune! ...

The nebula TRAPPIST-1 and company formed from was metal rich? Where'd ya hear that? Wikipedia lists the star's metallicity at just 0.04+/-0.08 dex. Very Sunlike.

Wikipedia wrote:
The star is metal-rich, with a metallicity ([Fe/H]) of 0.04, or 109% the solar amount. This is particularly odd as such low-mass stars near the boundary between brown dwarfs and hydrogen-fusing stars are expected to have considerably less metallic composition than the Sun.

Hey, I'm just quoting Wikipedia. :wink

BDanielMayfield wrote:...
Are they saying that the Sun is a metal rich star?

Doum wrote:
if it is billion years old or more then it change everything. Now that trappist-1 have attract our attention, his real age might be determine more precisely. Its a solar system that scientist will orbit around to study a lot. Im eager to see new publication about it.

On Feb. 22, astronomers announced that the ultra-cool dwarf star, TRAPPIST-1, hosts a total of seven Earth-size planets that are likely rocky, a discovery made by NASA's Spitzer Space Telescope in combination with ground-based telescopes. NASA's planet-hunting Kepler space telescope also has been observing this star since December 2016. Today these additional data about TRAPPIST-1 from Kepler are available to the scientific community.

During the period of Dec. 15, 2016 to March 4, the Kepler spacecraft, operating as the K2 mission, collected data on the star's minuscule changes in brightness due to transiting planets. These additional observations are expected to allow astronomers to refine the previous measurements of six planets, pin down the orbital period and mass of the seventh and farthest planet, TRAPPIST-1h, and learn more about the magnetic activity of the host star. ...

The release of the raw, uncalibrated data collected will aid astronomers in preparing proposals due this month to use telescopes on Earth next winter to further investigate TRAPPIST-1. By late May, the routine processing of the data will be completed and the fully calibrated data will be made available at the public archive. ...

Click to play embedded YouTube video.

A Resonant Dance of the Seven TRAPPIST-1 Planets
Credit: Daniel Fabrycky/University of Chicago

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Scientists using NASA's Kepler space telescope identified a regular pattern in the orbits of the planets in the TRAPPIST-1 system that confirmed suspected details about the orbit of its outermost and least understood planet, TRAPPIST-1h. ...

Astronomers from the University of Washington have used data from the Kepler spacecraft to confirm that TRAPPIST-1h orbits its star every 19 days. At six million miles from its cool dwarf star, TRAPPIST-1h is located beyond the outer edge of the habitable zone, and is likely too cold for life as we know it. The amount of energy (per unit) planet h receives from its star is comparable to what the dwarf planet Ceres, located in the asteroid belt between Mars and Jupiter, gets from our Sun. ...

Using the prior Spitzer data, the team recognized a mathematical pattern in the frequency at which each of the six innermost planets orbits their star. This complex but predictable pattern, called an orbital resonance, occurs when planets exert a regular, periodic gravitational tug on each other as they orbit their star. ...

These relationships, said Luger, suggested that by studying the orbital velocities of its neighboring planets, they could predict the exact orbital velocity, and hence also orbital period, of planet h, even before the Kepler observations. The team calculated six possible resonant periods for planet h that would not disrupt the stability of the system, but only one was not ruled out by additional data. The other five possibilities could have been observed in the Spitzer and ground-based data collected by the TRAPPIST team. ...

The Kepler spacecraft stared at the patch of sky home to the TRAPPIST-1 system from Dec. 15, 2016 to March 4 collecting data on the star’s minuscule changes in brightness due to transiting planets as part of its second mission, K2. On March 8, the raw, uncalibrated data was released to the scientific community to begin their follow-up studies.

The work to confirm TRAPPIST-1h’s orbital period immediately began and scientists from around the world took to social media to share in real-time the new information gleaned about the star’s behavior and its brood of planets. Within two hours of the data release, the team confirmed their prediction of a 19-day orbital period. ...

• Nature Astronomy 1:0129 (22 May 2017) DOI: 10.1038/s41550-017-0129
  arXiv.org > astro-ph > arXiv:1703.04166 > 12 Mar 2017

Astronomers from the University of Amsterdam (the Netherlands) explain with a model how seven earth-sized planets could have been formed in the planetary system Trappist-1. The crux is on the line where ice changes in water. (Image Credit: NASA/R. Hurt/T. Pyle)

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Astronomers from the University of Amsterdam have offered an explanation for the formation of the Trappist-1 planetary system. The system has seven planets as big as the Earth that orbit close to their star. The crux, according to the researchers from the Netherlands, is the line where ice changes to water. Near that ice line, pebbles that drifted from outer regions to the star receive an additional portion of water and clot together to form protoplanets. The article with the model has been accepted for publication in the journal Astronomy & Astrophysics.

In February 2017, an international team of astronomers announced the discovery of a system of seven exoplanets around a small star, Trappist-1. It was against the prevailing theories of planet formation that so many relatively large planets orbited so close around a small star. Researchers from the University of Amsterdam now come up with a model that explains how the planetary system could have originated.

Until now, there were two prevailing theories for the formation of planets. The first theory assumes that planets are formed more or less on the spot where they are now. With Trappist-1, that is unlikely because the disk from which the planets had originated should have been very dense. The second theory assumes that a planet forms much further out in the disk and migrates inward afterwards. This theory also causes problems with Trappist-1 because it does not explain why the planets are all about the same size as the Earth.

Now, the Amsterdam researchers come up with a model where pebbles migrate instead of complete planets. The model begins with pebbles that are floating from outside regions to the star. Such pebbles consist largely of ice. When the pebbles arrive near the so-called ice line, the point where it is warm enough for liquid water, they get an additional portion of water vapor to process. As a result, they clot together into a protoplanet. Then the protoplanet moves a little closer to the star. On its way it sweeps up more pebbles like a vacuum cleaner, until it reaches the size of the Earth. The planet then moves in a little further and makes room for the formation of the next planet.

The crux, according to the researchers, is in the clotting of pebbles near the ice line. By crossing the ice line, pebbles lose their water ice. But that water is re-used by the following load of pebbles that is drifting from the outer regions of the dust disk. At Trappist-1, this process repeated until seven planets were formed. ...

• Astronomy & Astrophysics (accepted 19 May 2017) DOI: 10.1051/0004-6361/201730826
  arXiv.org > astro-ph > arXiv:1703.06924 > 20 Mar 2017 (v1), 23 May 2017 (v3)