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Planet Hunters - TESS finds a habitable zone world orbiting a red dwarf star

Science Kiwi (MrElement)Jan 10, 2020, 10:08:45 AM
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As seen in header. Credit: NASA's Goddard Space Flight Center

NASA's Transiting Exoplanet Survey Satellite (TESS) has discovered its first Earth-size planet in its star's habitable zone, the range of distances where conditions may be just right to allow the presence of liquid water on the surface.

Out over 100 light years away is a cool red M dwarf star called TOI 700, with three orbiting planets. We can see it in the southern constellation called Dorado.

Red dwarf stars are the smallest and coolest kind of star on the main sequence. Red dwarfs are by far the most common type of star in the Milky Way, at least in our little neighborhood of the Sun, or Sol.

But because of their low luminosity, individual red dwarfs cannot be easily observed. This is where TESS and many of humanity's long range telescopes come in.

Proxima Centauri, the nearest star to the Sun, is a red dwarf; as are fifty of the sixty nearest stars. According to some estimates, red dwarfs make up three-quarters of the stars in the Milky Way! This might prove important to our search for life or habitable worlds amongst the stars.

The innermost planet, of the TOI 700 system, called TOI 700b, is almost exactly Earth-size, and is most likely rocky and completes an orbit every 10 days - a bit jarring to live on, mind you. Imagine a 10 day year ;) !

The middle planet, TOI 700c, is 2.6 times larger than Earth -- between the sizes of Earth and Neptune -- orbits every 16 days and is likely a gas-dominated world.

And then there's the last and outermost planet in the system, TOI 700d. This one is the one of most interest as it's the only one in the habitable zone, of the TOI 700 system.

TOI 700d measures 20% larger than Earth, orbits every 37 days and receives from its star 86% of the energy that the Sun provides to Earth. All of the planets are thought to be tidally locked to their star, which means they rotate once per orbit so that one side is constantly bathed in daylight.

On the upside - you can travel to one side of the planet and be always guaranteed sunbathing conditions!

A team of scientists led by Joseph Rodriguez, an astronomer at the Center for Astrophysics | Harvard & Smithsonian in Cambridge, Massachusetts, requested follow-up observations with Spitzer to confirm TOI 700 d.

Given the impact of this discovery -- that it is TESS's first habitable-zone Earth-size planet -- we really wanted our understanding of this system to be as concrete as possible," Rodriguez said. "Spitzer saw TOI 700 d transit exactly when we expected it to. It's a great addition to the legacy of a mission that helped confirm two of the TRAPPIST-1 planets and identify five more.

The Spitzer data increased scientists' confidence that TOI 700 d is a real planet and sharpened their measurements of its orbital period by 56% and its size by 38%. It also ruled out other possible astrophysical causes of the transit signal, such as the presence of a smaller, dimmer companion star in the system.

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