Three Potential Earth-like Planets Discovered Around Nearby Star

This artist’s impression shows an imagined view from the surface one of the three planets orbiting an ultracool dwarf star just 40 light-years from Earth that were discovered using the TRAPPIST telescope at ESO’s La Silla Observatory. These worlds have sizes and temperatures similar to those of Venus and Earth and are the best targets found so far for the search for life outside the Solar System. They are the first planets ever discovered around such a tiny and dim star. In this view one of the inner planets is seen in transit across the disc of its tiny and dim parent star. Credit: ESO/M. Kornmesser
This artist’s impression shows an imagined view from the surface one of the three planets orbiting an ultracool dwarf star just 40 light-years from Earth that were discovered using the TRAPPIST telescope at ESO’s La Silla Observatory in Chile. They have sizes and temperatures similar to those of Venus and Earth and are the best targets found so far for the search for life outside the Solar System. In this view one of the inner planets is seen in transit across the disc of its tiny and dim parent star. Credit: ESO/M. Kornmesser

Three new planets discovered around a tiny, faint star in the constellation Aquarius may be among the best places to look for evidence of extraterrestrial life. A team of astronomers led by Michaël Gillon of the Institute of Astrophysics and Geophysics at the University of Liege in Belgium studied the star, named TRAPPIST-1, and discovered it faded in regular cycles. Analysis of the repeated dips in brightness revealed that three planets all about the size of the Earth orbiting the star were responsible.

This picture shows the Sun and the ultracool dwarf star TRAPPIST-1 to scale. The faint star has only 11% of the diameter of the sun and is much redder in colour. It's less the 0.08% as massive as the sun. Credit: ESO
This picture shows the sun and the dwarf star TRAPPIST-1 (a.k.a. 2MASS J23062928-0502285) to scale. The faint star is just 11% the the diameter of the sun, 8% as massive and a much redder color. Though relatively near Earth, it’s so faint that even a large amateur telescope won’t show it. Credit: ESO

TRAPPIST-1 is an ultra-cool red dwarf star only a little larger than Jupiter located 40 light years from Earth. Red dwarfs are far less massive than the sun and are probably the most common type of star in the galaxy. They burn their nuclear fuel so frugally, dwarfs have long lifetimes measured in the trillions of years compared to the 10-billions lifetimes allotted to larger stars like our sun that devour their fuel more quickly. This is the first time that planets have been found around one of them.

Emmanuël Jehin, a co-author of the new study, is excited: “This really is a paradigm shift with regards to the planet population and the path towards finding life in the universe. So far, the existence of such ‘red worlds’ orbiting ultra-cool dwarf stars was purely theoretical, but now we have not just one lonely planet around such a faint red star but a complete system of three planets!”

This artist’s impression shows an imagined view of the three planets orbiting an ultracool dwarf star just 40 light-years from Earth that were discovered using the TRAPPIST telescope at ESO’s La Silla Observatory. These worlds have sizes and temperatures similar to those of Venus and Earth and may be the best targets found so far for the search for life outside the Solar System. They are the first planets ever discovered around such a tiny and dim star. In this view one of the inner planets is seen in transit across the disc of its tiny and dim parent star. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org)
This artist’s impression shows an imagined view of the three planets orbiting TRAPPIST-1 just 40 light-years from Earth. They are the first planets ever discovered around such a tiny and dim star. In this view one of the inner planets is seen in transit across the disc of its tiny and dim parent star. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org)

Nearly all of the 2,111 extrasolar planets discovered to date orbit brighter stars. Astronomers search for signs of life by looking for fingerprints of life-related gases like oxygen, methane and water vapor when light from the host star passes through the atmosphere of a transiting planet. For Earth-sized planets orbiting most stars this tiny effect is swamped by the brilliance of the starlight. Only for the case of faint red ultra-cool dwarf stars like TRAPPIST-1 is this effect big enough to be detected.

Follow-up observations with larger telescopes, including the European Southern Observatory’s (ESO) 8-meter (315-inch) Very Large Telescope in Chile, have shown that the planets orbiting the dwarf have sizes very similar to that of Earth. Two of the planets orbit the star about every 1.5 days and 2.4 days respectively, and the third planet somewhere in the range of 4.5 to 73 days.

This chart shows the naked eye stars visible on a clear dark night in the sprawling constellation of Aquarius (The Water Carrier). The position of the faint and very red ultracool dwarf star TRAPPIST-1 is marked. Although it is relatively close to the Sun it is very faint and not visible in small telescopes. Credit: ESO/IAU and Sky & Telescope
This chart shows the location of TRAPPIST-1 in eastern Aquarius. Although relatively close to the Sun it’s very faint and not visible in small telescopes. Credit:ESO/IAU, Sky & Telescope

Those short orbital periods indicate that the planets are between 20 and 100 times closer to their star than the Earth to the sun. Despite that proximity, the inner two planets only receive four time and twice the amount of radiation received by the Earth because TRAPPIST-1 is so much fainter than the sun. The same way you or I might huddle closer to a small fire to soak up its heat, the three planets’ close orbits ensures they feel their star’s warmth.

They might even be a little too close; astronomers place them just outside the “habitable zone”, the region around a star where a rocky planet with a thick enough atmosphere can support liquid water on its surface. That’s doesn’t rule out regions on their surfaces that might be clement, but only time and further observations will tell. Scale-wise, Gillon compares the system to Jupiter and its moons.

The full-scale model was assembled on the lawn at Goddard Space Flight Center, and displayed during September 19 - 25 2005. The Webb Telescope team took a group photo with it. Seeing the people gathered next to it shows its scale nicely. Credit: NASA
The full-scale model was assembled on the lawn at Goddard Space Flight Center, and displayed during September 19 – 25 2005. Seeing the people gathered next to it shows its scale nicely. Credit: NASA

We shouldn’t have to wait long to find out if any of the three possesses water or possible traces of biological activity. The European Extremely Large Telescope, a 39-meter (1,535-inch) expected to see first light in 2024, and the James Webb Space Telescope, set to launch in 2018, will have the firepower to study their atmospheric compositions.

Since about 15% of the stars near the sun are ultra-cool dwarfs — I can’t shake the image of stars wearing sunglasses — we’re only beginning to knock on the doors of Earth’s cousins.