Using a telescope specifically designed to hunt for exoplanets, a team of astronomers working at the European Southern Observatory (ESO) has discovered three planets orbiting a dwarf sun just 40 light-years from Earth. According to the researchers, all three worlds are potentially habitable given their sizes and temperatures, and may be the best candidates yet in the search for life beyond our solar system.
Using the TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) instrument at ESO's La Silla station located near the ALMA complex in the Atacama Desert, Chile, astronomers spotted spotted the three worlds rotating around an ultracool red dwarf star dubbed 2MASS J23062928-0502285, but now also known as TRAPPIST-1.
Subsequent observations using more powerful telescopes, including ESO's 8-meter (26-ft) Very Large Telescope HAWK-I near-infrared instrument located nearby, have confirmed that the planets spinning around TRAPPIST-1 appear to be close in size to Earth. Two of the planets have well-defined orbital periods of around 1.5 days, and 2.4 days, whilst the third planet seems to be somewhat less stable, with an orbital period that varies widely between 4.5 to 73 days.
"This really is a paradigm shift with regards to the planet population and the path towards finding life in the Universe," said Emmanuël Jehin, from the Institut d'Astrophysique et Géophysique at the University of Liège in Belgium and Research Associate on the TRAPPIST team. "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!"
Defined as an ultracool dwarf star, TRAPPIST-1 is significantly cooler and redder than our own sun, and is not much bigger than Jupiter. Far too dim to be observed without a very large telescope, the small star is situated in the constellation of Aquarius visible at latitudes between +65° and −90°. According to the astronomers, such stars are very common in our Milky Way as well as being exceptionally long-living, however this is claimed to be the very first time that one has been discovered with planets in orbit around it.
Though these worlds have sizes and temperatures similar to those of Venus and Earth, two of them are in very close orbit to their parent star, which means that they are closer to their sun than habitable zone requirements normally allow. However, because the star is so much fainter than the Sun, the researchers believe it is still possible the two inner planets may have habitable areas on their surfaces. The furthest of the two inner planets receives approximately twice the radiation received by the Earth and the inner one four times as much.
The third and outermost planet has an orbit that still appears erratic, but the team believes that at its farthest point it is probably less irradiated than the Earth, but could still receive enough radiation to put it in the habitable zone.
"With such short orbital periods, the planets are between 20 and 100 times closer to their star than the Earth to the Sun," said Michaël Gillon, also from the Institut d'Astrophysique et Géophysique at the University of Liège in Belgium and Research Associate on the TRAPPIST team. "The structure of this planetary system is much more similar in scale to the system of Jupiter's moons than to that of the Solar System."
Ongoing studies of these newly-found planets will include the search for signs of life by examining the atmosphere of the planets as they transit their star. Light passing through the gases in these atmospheres will provide an indication as to their chemical make-up and, as the red dwarf will not swamp the planet in its brilliance as normal bright stars do, the researchers believe that they will have a much better chance of ascertaining the compositions of the gases present.
"Thanks to several giant telescopes currently under construction, including ESO's E-ELT and the NASA/ESA/CSA James Webb Space Telescope due to launch for 2018, we will soon be able to study the atmospheric composition of these planets and to explore them first for water, then for traces of biological activity," said Julien de Wit, a co-author on the research from MIT. "That's a giant step in the search for life in the Universe."
According to the TRAPPIST team, this type of research will help to open up new avenues in the search for exoplanets, as approximately 15 percent of the stars in reasonable proximity to our solar system are ultra-cool dwarf stars. This area of exoplanet hunting also shows that it is possible to find and analyze potential habitable planets that are similar in many respects to our own Earth, even around cool dwarf stars.
"Why are we trying to detect Earth-like planets around the smallest and coolest stars in the solar neighbourhood? " asks Gillon. "The reason is simple: systems around these tiny stars are the only places where we can detect life on an Earth-sized exoplanet with our current technology. So if we want to find life elsewhere in the Universe, this is where we should start to look."
The team's research paper on their discovery was recently published by the European Southern Observatory team, and the PDF can be accessed here.
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