A red sun rises, huge and blazing hot in the sky. Then another sun rises, smaller and farther away. And then, quickly, a third distant sun. Morning has broken on the planet LTT 1445Ab, and it may be the easiest place outside our solar system to look for signs of life.
Astronomers used the Transiting Exoplanet Survey Satellite (TESS), a space telescope that looks for planets orbiting distant stars, to spot LTT 1445Ab in a triple-star system 22.5 light years away. They caught it as it passed in front of one of the stars in the system four times in late 2018. It鈥檚 the second-closest planet to us that鈥檚 been found using this method.
Observations with TESS and a number of ground-based telescopes revealed that LTT 1445Ab is orbiting the primary star of the system, or A, while the other two stars 鈥� B and C 鈥� orbit A together at a distance of billions of kilometres.
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鈥淚f you鈥檙e standing on the surface of that planet, there are three suns in the sky, but two of them are pretty far away and small-looking,鈥� says team member Jennifer Winters at the Harvard-Smithsonian Center for Astrophysics in Massachusetts. 鈥淭hey鈥檙e like two red, ominous eyes in the sky.鈥�
The planet circles A once every 5.4 Earth days at a distance of about 5.7 million kilometres, about the same as the distance between Mercury and the sun. At a radius about 1.3 times Earth鈥檚, this world is small enough to be rocky, and its red star is just bright enough to backlight it but not so bright that the planet is difficult to spot.
Its relative closeness to us聽and that perfect lighting mean that if it has an atmosphere, LTT 1445Ab is the perfect candidate for examining how that atmosphere changes the starlight that shines through it, which can tell us what the atmosphere is made of. Some gases, like oxygen and methane, may point to biological origins.
鈥淚t鈥檚 the best place that we know of so far to look for signs of life in an atmosphere,鈥� says Winters. 鈥淲e don鈥檛 know yet聽if there鈥檚 an atmosphere, and it may be too hot for life, but we鈥檙e hopeful because this is our best chance so far.鈥�
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