TESS finds its first Earth-sized planet

TESS finds its first Earth-sized planet
Artist's conception of HD 21749c, the first Earth-sized planet found by NASA's Transiting Exoplanets Survey Satellite (TESS), as well as its sibling, HD 21749b, a warm sub-Neptune-sized world. Credit: Robin Dienel, courtesy of the Carnegie Institution for Science

A nearby system hosts the first Earth-sized planet discovered by NASA's Transiting Exoplanets Survey Satellite, as well as a warm sub-Neptune-sized world, according to a new paper from a team of astronomers that includes Carnegie's Johanna Teske, Paul Butler, Steve Shectman, Jeff Crane, and Sharon Wang.

Their work is published in the Astrophysical Journal Letters.

"It's so exciting that TESS, which launched just about a year ago, is already a game-changer in the planet-hunting business," said Teske, who is second author on the paper. "The spacecraft surveys the sky and we collaborate with the TESS follow-up community to flag potentially interesting targets for additional observations using ground-based telescopes and instruments."

One such tool, the Planet Finder Spectrograph on the Magellan II telescope at Carnegie's Las Campanas Observatory in Chile, was a crucial component of this effort. It helped confirm the planetary nature of the TESS signal, and to measure the mass of the newly discovered sub-Neptune.

The PFS—built by Shectman and Crane using a method pioneered by Butler and his collaborators—works using a technique called the , which is currently the only way for astronomers to measure the masses of individual planets. Without known masses, it is very challenging to determine a planet's density or its general chemical composition.

This method takes advantage of that fact that not only does a star's gravity influence the planet orbiting it, but the planet's gravity also affects the star in turn. The PFS enables astronomers to detect these tiny wobbles that the planet's gravity induces in the star's orbit.

"PFS is one of the only instruments in the Southern Hemisphere that can do these types of measurements," Teske added. "So, it will be a very important part of further characterizing the planets found by the TESS mission."

With an orbit that takes about 36 days to complete, the sub-Neptune, HD 21749b, has the longest period of any of the TESS discoveries published so far. Because of the technique that TESS employs, it is predicted that most of the planets the mission finds will have orbital periods of fewer than 10 days, so HD 21749b is unusual in this regard. In fact, this also made the detection of the planet in the TESS data an extra challenge.

"There was quite some detective work involved, and the right people were there at the right time," said lead author Diana Dragomir of MIT's Kavli Institute for Astrophysics and Space Research. "But we were lucky, and we caught the signals, and they were really clear."

Its host star has about 80 percent of the mass of our Sun and is found about 53 light-years distant from Earth. HD 21749b has about 23 times Earth's mass and a radius of about 2.7 times Earth's. Its density indicates the planet has substantial atmosphere but is not rocky, so it could potentially help astronomers understand the composition and evolution of cooler sub-Neptune planet atmospheres.

Excitingly, the longer period sub-Neptune planet in this system is not alone. It has a sibling planet, HD 21749c, which takes about eight days to orbit the host star and is much smaller—similar in size to Earth.

"Measuring the exact mass and composition of such a small planet will be challenging, but important for comparing HD 21749c to Earth," said Wang. "Carnegie's PFS team is continuing to collect data on this object with this goal in mind."

Thanks to TESS, astronomers will be able to measure the masses, atmospheric compositions, and other properties of many smaller exoplanets for the first time. Although small exoplanets are common in our galaxy, there is still much to learn about their diversity and about how they compare to the planets in our own Solar System.

"For stars that are very close by and very bright, we expected to find up to a couple dozen Earth-sized planets," said Dragomir. "And here we are—this would be our first one, and it's a milestone for TESS. It sets the path for finding smaller planets around even smaller stars, and those may potentially be habitable."

Explore further

An exoplanet with an 11-hour orbit

More information: Diana Dragomir et al, TESS Delivers Its First Earth-sized Planet and a Warm Sub-Neptune, The Astrophysical Journal (2019). DOI: 10.3847/2041-8213/ab12ed
Citation: TESS finds its first Earth-sized planet (2019, April 15) retrieved 20 April 2019 from https://phys.org/news/2019-04-tess-earth-sized-planet.html
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Apr 15, 2019
Not SAID in the above article about how happy we are to find nice warm fuzzy neighbors is that given the central star's size and the short periods of the foundlings, They probably have clouds that rain iron and lead.....in ..liquid...form.

Do not think anyone will find that a hospitable place. Only use our starfaring neighbors will have of it is to skim that thick atmosphere for mining purposes...from the safety of space and at high velocities with large Boussard collectors.

Apr 15, 2019
""And here we are—this would be our first one, and it's a milestone for TESS. It sets the path for finding smaller planets around even smaller stars, and those planets may potentially be habitable.""

This is all nice to discover, catalogue and dream that 'some day' humans might have the abilities to visit such places "out there". But spacefaring humans might only be limited to the planets and moons in the Solar System, due to many limitations that are physically and mentally restrictive.
The Earth gave rise to the human species/race and is most suited in every way for humans, animals and plants to thrive; so that it may be idealistic to expect the eventual conquering of exoplanets by humans, but expectations are often rebuffed by Reality.
And the Earth is what you know and love and couldn't get along without. It is home. Take good care of it and it will always feel good to come home.

Apr 15, 2019
Is this the planet a planet hunter found?
where one year equals 36 earth days
how long does this planet take to rotate
as that will be its day
suppose it rotates once every 36 earth days
can you imagine
being in the dark for 18 earth days
there are a lot more reasons why life has evolved on earth than simply temperature
if animals have to live alternately day and night
8 hours of dark for 16 hour of light works
try 6months of darkness where temperatures drop and nothing grows
our planet is what should be being sought in this galaxy
we know life evolves on our planet and not on mars type of planets

Apr 15, 2019
suppose it rotates once every 36 earth days
can you imagine
being in the dark for 18 earth days

No, if it has a year of 36 days, and its rotates once on its axis every 36 days, it will show the same face to its star permanently. It will be what is termed 'tidally locked'. Just as the Moon is with the Earth. If it didn't rotate at all one side would experience some prolonged darkness.

Apr 15, 2019
And there is no way this planet, or its companion, could be considered habitable. The larger one orbits at ~ 0.19 AU, and has an equilibrium temperature of ~ 420 K (~ 150 C). Its smaller companion is even hotter. And the larger planet has no solid surface.

Apr 15, 2019
Life on the Darkside

Tidally locked
Its host star
which has 80 percent of the mass of our Sun
orbiting in 36 days
even with its detected atmosphere
this planet orbiting 10x faster than earth
so as if
if nothing else it is warm
with plenty of solar storms and coronal mass ejections
massive thunderstorms in the thick atmosphere
it is starting to sound
A very active planet with extremes of temperature, to its dark side

Apr 15, 2019
^^^^Good thing I'm here to continually correct your misunderstandings, isn't it?

Apr 15, 2019
TESS on the Darkside

The whole point
was not simply planet hunting
that is easy
as there are billions of planets
it is earth like habitable planets we crave
A planet that makes our sunburn look like suncream

Apr 15, 2019
Planet Hunting on the Darkside

I was searching its daily spin
^^^^Good thing I'm here to continually correct your misunderstandings, isn't it?

and it 36 days was problematic
we can only hope this is not the best
That TESS is finding, because there are billions of planets exactly like these

Apr 15, 2019
^^^^^Granville, just give up, yes? This is essentially a proof of concept observation. It can detect these planets. That is all.

Apr 15, 2019
jonesy> ^^^^^Granville, just give up, yes? This is essentially a proof of concept observation. It can detect these planets. That is all.

jonesy, your request will be granted sooner than you think
jonesy, phys.org is changing
that in time jonesy
as you sit all alone at you empty keyboard
because phys.org is this last one
so unless you find another jonesy your wish will be granted
and sooner if you keep up your style
Good luck in your quest, jonesy

Apr 16, 2019
Surveilence clown antigoracle sockpuppet learned the art of surveying himself, yet still don't understand himself ;)we love the monkey comments

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