Exoplanets – worlds of other suns

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TESS discovery of a super-Earth and two sub-Neptunes orbiting the bright, nearby, Sun-like star HD 22946
https://arxiv.org/abs/2209.09597

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HD 23472: A multi-planetary system with three super-Earths and two potential super-Mercuries
https://arxiv.org/abs/2209.13345

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Newly Discovered ‘Super-Earth’ Planet May Be Able to Support Life
by Madeleine Muzdakis
September 27, 2022

Extract:

(MY Modern Met) The University of Liège researchers…through their advanced telescope nicknamed SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars)…spotted (a super-Earth planet).. known as LP 890-9b, is 30% larger than Earth and orbits its own sun in 2.7 days. (A)… second (planet) was dubbed LP 890-9c (or SPECULOOS-2c). It is 40% larger than Earth with an orbit of 8.5 days.

Francisco Pozuelos, of the Institute of Astrophysics of Andalusia and co-author of a recent paper on the planets, indicated in a statement that SPECULOOS-2c could potentially sustain life. While it is only 3.7 million miles from its sun—versus Earth's 93 million mile distance—the planet's environment may be able to maintain liquid water. “Although this planet orbits very close to its star, at a distance about 10 times shorter than that of Mercury around our Sun, the amount of stellar irradiation it receives is still low, and could allow the presence of liquid water on the planet's surface, provided it has a sufficient atmosphere,” Pozuelos says.

“This is because the star LP 890-9 [the exoplanet's sun] is about 6.5 times smaller than the Sun and has a surface temperature half that of our star.” While it may be presently unclear whether life exists on the super-Earth, the find itself is exciting.

Read more here: https://mymodernmet.com/super-earth-speculoos/

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Discovery Alert: A Rocky 'Super-Earth' in the Habitable Zone
https://exoplanets.nasa.gov/news/1712/d ... PVwk8gpye4
By Pat Brennan, NASA's Exoplanet Exploration Program

The discovery: LP 890-9 c, a “super-Earth” in the habitable zone of its star.

Key facts: The planet, likely rocky but 40% larger than Earth, came to light during follow-up observations of its sister planet, LP 890-9 b. Both fall into the super-Earth category – exoplanets, or planets around other stars, that are up to 75% larger than our own but believed to be rocky worlds, like Earth. Surface conditions might or might not be similar.
The latest

Details: Both planets orbit a comparatively cool, red-dwarf star, LP 890-9, about 98 light-years away. The inner planet, discovered using the Transiting Exoplanet Survey Satellite (TESS), is about 30% larger than Earth and, with an estimated temperature of 253 degrees Fahrenheit (123 Celsius), probably too hot to be habitable. The outer planet, though possibly chilly by human standards at an estimated 30 Fahrenheit (minus 1.1 Celsius), sits within its star’s habitable zone, the orbital distance where liquid water might be present on the surface. This planet was detected using a ground-based telescope survey, the Search for habitable Planets EClipsing Ultra-cOOl Stars (SPECULOOS). The observations not only met their original goal – confirming the existence of the innermost planet – but unexpectedly discovered a second planet in the system.

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Heaviest Element Yet Detected In Exoplanet Atmospheres Where It Rains Iron And Jewels
by Dr Alfredo Carpineti
October 14, 2022

Introduction:

(IFL Science) Astronomers have discovered something puzzling in the atmospheres of two exoplanets: barium. The 56th member of the periodic table is the heaviest element ever discovered in the atmosphere of an exoplanet, detected in the upper layers of two peculiar worlds, both ultra-hot Jupiters: WASP-76 b and WASP-121 b. And we're not exaggerating when we say peculiar. Scientists think it rains iron on WASP-76b, and liquid sapphires and rubies might be falling on the night side of WASP-121b.

These gas giant exoplanets orbit extremely close to their stars, much closer than Mercury is to the Sun. They reach incredible temperatures of over 1,000°C (1800°F), hot enough to melt and vaporize metals, including barium. Although it's unclear how the barium got so high up, given that it is 2.5 times heavier than iron.

“The puzzling and counterintuitive part is: why is there such a heavy element in the upper layers of the atmosphere of these planets?” lead author Tomás Azevedo Silva, of the University of Porto and the Institute of Astrophysics and Space Sciences in Portugal, said in a statement.

“Given the high gravity of the planets, we would expect heavy elements like barium to quickly fall into the lower layers of the atmosphere,” added co-author Olivier Demangeon, a researcher in the same institutions.

The presence of barium and the question of how it was transported to the upper atmosphere suggests that we might understand less about these planets’ atmospheres than we previously thought. Ultra-hot Jupiters are inflated due to their high temperatures which are extremely advantageous to study their atmospheres.

Read more here: https://www.iflscience.com/heaviest-el ... els-65762

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Three Red Suns in the Sky: A Transiting, Terrestrial Planet in a Triple M Dwarf System at 6.9 Parsecs
https://arxiv.org/abs/1906.10147

We present the discovery from TESS data of LTT 1445Ab. At a distance of 6.9 parsecs, it is the second nearest transiting exoplanet system found to date, and the closest one known for which the primary is an M dwarf. The host stellar system consists of three mid-to-late M dwarfs in a hierarchical configuration, which are blended in one TESS pixel. We use follow-up observations from MEarth and the centroid offset analysis in the TESS data validation report to determine that the planet transits the primary star in the system. The planet has a radius 1.35 R_Earth, an orbital period of 5.35882 days, and an equilibrium temperature of 428 K. With radial velocities from HARPS, we place a three-sigma upper mass limit of 8.4 M_Earth on the candidate. The planet provides one of the best opportunities to date for the spectroscopic study of the atmosphere of a terrestrial world. The presence of stellar companions of similar spectral type may facilitate such ground-based studies by providing a calibration source to remove telluric variations. In addition, we present a detailed characterization of the host stellar system. We use high-resolution spectroscopy and imaging to rule out the presence of any other close stellar or brown dwarf companions. Nineteen years of photometric monitoring of A and BC indicates a moderate amount of variability, in agreement with the observed low-level, short-term variability in the TESS light curve data. We derive a preliminary astrometric orbit for the BC pair that reveals an edge-on and eccentric configuration. The presence of a transiting planet in this system raises the possibility that the entire system is co-planar, which implies that the system may have formed from the early fragmentation of an individual protostellar core.

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Three Red Suns in the Sky: A Transiting, Terrestrial Planet in a Triple M Dwarf System at 6.9 Parsecs
https://arxiv.org/abs/1906.10147

We present the discovery from TESS data of LTT 1445Ab. At a distance of 6.9 parsecs, it is the second nearest transiting exoplanet system found to date, and the closest one known for which the primary is an M dwarf. The host stellar system consists of three mid-to-late M dwarfs in a hierarchical configuration, which are blended in one TESS pixel. We use follow-up observations from MEarth and the centroid offset analysis in the TESS data validation report to determine that the planet transits the primary star in the system. The planet has a radius 1.35 R_Earth, an orbital period of 5.35882 days, and an equilibrium temperature of 428 K. With radial velocities from HARPS, we place a three-sigma upper mass limit of 8.4 M_Earth on the candidate. The planet provides one of the best opportunities to date for the spectroscopic study of the atmosphere of a terrestrial world. The presence of stellar companions of similar spectral type may facilitate such ground-based studies by providing a calibration source to remove telluric variations. In addition, we present a detailed characterization of the host stellar system. We use high-resolution spectroscopy and imaging to rule out the presence of any other close stellar or brown dwarf companions. Nineteen years of photometric monitoring of A and BC indicates a moderate amount of variability, in agreement with the observed low-level, short-term variability in the TESS light curve data. We derive a preliminary astrometric orbit for the BC pair that reveals an edge-on and eccentric configuration. The presence of a transiting planet in this system raises the possibility that the entire system is co-planar, which implies that the system may have formed from the early fragmentation of an individual protostellar core.

This isn't new, though. Published June 2019.

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Gas Giant Planet With Density of a Marshmallow Breaks All The Rules
by Stephen Luntz
October 21, 2022

Introduction:

(IFL Science) Patterns have emerged in the thousands of planets recently discovered orbiting stars besides the Sun. So when planets are found that break those patterns, astronomers get curious, particularly when they have been confident in their explanations for what they have seen.

The latest rule-breaker goes by the not-exactly rebellious-sounding name of TOI-3757 b and lies 580 light-years away in the constellation Auriga. Its radius is 10 percent greater than Jupiter’s, but its mass is barely a quarter as great. In fact, it's the lowest-density gas giant ever found orbiting a red dwarf.

Saturn famously has a density lower than water, leading to children’s astronomy books sometimes picturing It floating on an immense ocean. TOI-3757 b is 60 percent less dense still; just 0.27 grams per cubic centimeter (0.037 pounds per cubic foot). The astronomers who found it have compared it to a marshmallow, so perhaps we need a giant hot chocolate in which it can bob.

Light as it is, if TOI-3757 b was orbiting a more Sun-like star it wouldn’t stand out. However, gas giants are rare around red dwarfs to start off with – just 10 have been found, 0.2 percent of known planets, so one so insubstantial requires explanation.

One clue to TOI-3757 b’s likely formation lies in the fact its parent star, TOI-3757, has the lowest metal abundance (astronomically defined as anything heavier than helium) of the red dwarfs known to have giant planets. The composition of the disk from which planets form reflects that of the star, so it’s likely heavier elements were in short supply when TOI-3757 b formed.

Read more here: https://www.iflscience.com/gas-giant-p ... les-65879

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A Nearby Star Has Completely Blasted Away the Atmosphere From its Planet
by Carolyn Collins Petersen
October 22, 2022

Introduction:

(Universe Today) What if you placed an Earth-sized planet in a close orbit around an M-dwarf star? It’s more than an academic question since M dwarfs are the most numerous stars we know. A group of astronomers studying the planet GJ 1252b found an answer and it’s not pretty.

Since this planet is so close to its star, it receives a lot of heat. And that proximity is deadly in another way. “The pressure from the star’s radiation is immense, enough to blow a planet’s atmosphere away,” said Michelle Hill, a University of California Riverside astrophysicist and co-author of a recent paper focused on GJ 1252b. The planet lies some 65 light-years from Earth and orbits its star twice every 24 Earth hours. The heat from the star renders this world inhospitable.

This is not terribly different from Mercury in our solar system. There’s no atmosphere and the planet is alternately heated and frozen as it orbits the Sun. In fact, Earth also loses a little atmosphere to solar activity. However, volcanism and other processes release gases back into our atmosphere. Earth is lucky; planets like Mercury and GJ 1252b are not. And, that has profound implications in the search for life-friendly worlds.

Read more here: https://www.universetoday.com/158217/a ... re-158217



Illustration of the atmosphere being blown away from a planet by a nearby star.
NASA

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Ways JWST Could Detect Alien Life
by Matt Williams
October 27, 2022

Introduction:

(Universe Today) Less than a year after it went to space, the James Webb Space Telescope (JWST) has already demonstrated its worth many times over. The images it has acquired of distant galaxies, nebulae, exoplanet atmospheres, and deep fields are the most detailed and sensitive ever taken. And yet, one of the most exciting aspects of its mission is just getting started: the search for evidence of life beyond Earth. This will consist of Webb using its powerful infrared instruments to look for chemical signatures associated with life and biological processes (aka. biosignatures).

The chemical signatures vary, each representing a different pathway toward the potential discovery of life. According to The Conversation’s Joanna Barstow, a planetary scientist and an Ernest Rutherford Fellow at The Open University specializing in the study of exoplanet atmospheres, there are four ways that Webb could do this. These include looking for chemicals that lifeforms depend on, chemical byproducts produced by living organisms, chemicals essential to maintaining a stable climate, and chemicals that shouldn’t coexist.

In their search for life beyond Earth, astrobiologists have been restricted to the “low-hanging fruit” approach. This consists of searching for terrestrial (or rocky) planets that orbit within their parent stars’ circumsolar habitable zones (HZs) or the distance where planets will be warm enough to maintain liquid water on their surfaces. With next-generation telescopes like Webb, which combine sensitive optics, coronographs, and spectrometers with near- and mid-infrared imaging capability, the field of exoplanet study is transitioning from discovery to characterization.

As we explored in previous articles, this involves direct imaging studies of exoplanets and obtaining spectroscopic data from their atmospheres. Since the early 19th century, scientists have known that certain chemical elements absorb light at certain wavelengths and radiate it in others. By performing a “chemical inventory” of exoplanet atmospheres, astrobiologists will be able to place much tighter constraints on exoplanet habitability. In other words, they will be able to say with much greater confidence if a planet is habitable (and not just “potentially habitable”).

Read more here: https://www.universetoday.com/158228/h ... re-158228

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New exoplanet detected with the ESPRESSO spectrograph

by Tomasz Nowakowski , Phys.org
https://phys.org/news/2022-11-exoplanet ... graph.html

Using the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO), astronomers from Switzerland and Austria have discovered a new alien world. The newfound exoplanet orbits a nearby M dwarf star and is at least four times more massive than the Earth. The finding is reported in a paper published October 23 on arXiv.org.

ESPRESSO is the state-of-the-art ultra-stable high resolution spectrograph installed at the Very Large Telescope (VLT) in Chile, covering the spectral range from about 380 nm to 788 nm. The instrument is able to reach a precision allowing it to detect Earth-like planets around sun-like stars.

A team of astronomers led by Lia F. Sartori of the Swiss Federal Institute of Technology in Zürich, Switzerland, is conducting a blind ESPRESSO radial velocity search for planets around nearby stars. One of their targets was L 363-38—an M dwarf located some 33.3 light years away. They monitored this star between December 12, 2020 and February 08, 2022, obtaining a total of 31 observations, which resulted in the detection of a new planet.

"In the following we report the detection and characterization of a planet orbiting the nearby M dwarf star L 363-38. This is one of the few standalone planet discoveries with ESPRESSO so far," the researchers wrote in the paper.

The newly detected planet, designated L 363-38 b, has a minimum mass of about 4.67 Earth masses and its radius is estimated to be between 1.55 and 2.75 Earth radii. The exoplanet orbits its host every 8.78 days, at a distance of some 0.048 AU from it, therefore inside the inner edge of the habitable zone. The equilibrium temperature of L 363-38 b was calculated to be approximately 330 K.

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Many planets could have atmospheres rich in helium, study finds
https://phys.org/news/2022-11-planets-a ... elium.html
by Louise Lerner, University of Chicago

For centuries, no one knew if we were alone in the universe—or if there were even other planets like ours.

But thanks to new telescopes and methods in the past decades, we now know there are thousands and thousands of planets out there circling faraway stars, and they come in all sorts of shapes and sizes—large and small, rocky and gaseous, cloudy or icy or wet.

A study by scientists with the University of Chicago, the University of Michigan and the University of Maryland suggests another for the list: planets with helium atmospheres. Moreover, the discovery may suggest a new step in our understanding of planet evolution.

Their simulations found that it's likely that helium would build up in the atmospheres of certain types of exoplanets over time. If confirmed, this would explain a decades-long puzzle about the sizes of these exoplanets.

"There are so many weird and wonderful kinds of exoplanets out there, and this finding not only adds a new kind but may have implications for understanding the evolution and formation of planets in general," said University of Chicago astrophysicist Leslie Rogers, a co-author of the new paper published in Nature Astronomy.

Mystery of the radius valley

It took us so long to find faraway planets because even the biggest are far outshone by the stars they orbit. So scientists came up with an ingenious way to spot them: by looking for the dip in the light of a star as a planet passes in front of it. This tells you how large the planet is.

Now we know planets are incredibly common. In fact, from what we can tell so far, at least half of all stars like our sun have at least one planet between the size of Earth and Neptune that orbits very close to the star. It's hypothesized these planets have atmospheres with a lot of hydrogen and helium, collected when the planets first formed out of gas and dust around the star.

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“Hell Planet” Orbits Its Sun Every 17.5 Hours
by Jim Shelton
December 9, 2022

Introduction:

(Futurity) New technology has helped astronomers follow the fiery trail of the so-called “hell planet.”

It’s an exoplanet located 40 light years from Earth and nicknamed for its extremely close orbit to its sun.

Debra Fischer, a professor of astronomy at Yale University, developed the instrument that enabled the work, which is housed at the Lowell Observatory’s Lowell Discovery Telescope in Arizona.

The EXtreme PREcision Spectrometer (EXPRES), has captured ultra-precise measurements of the starlight from the distant planet’s sun. Astronomers have now analyzed those measurements to determine the orbit of planet 55 Cnc e.

55 Cnc e, which was discovered in 2004, is so hot (roughly 3,600 degrees Fahrenheit) that its surface is an ocean of lava.

Read more here: https://www.futurity.org/hell-planet-orbit-2843032/

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Two Temperate Earth-mass Planets Orbiting The Nearby Star GJ1002
By Keith Cowing
https://astrobiology.com/2022/12/two-te ... j1002.html
December 14, 2022

Filed under astro-ph.EP, CARMENES, ESPRESSO, exoplanet, extrasolar, GJ~1002, Habitable Zone, M5.5~V, Spectrograph, TESS
Two Temperate Earth-mass Planets Orbiting The Nearby Star GJ1002

Two-planet model. Top panels: Combined FWHM time series of ESPRESSO and CARMENES with the best fit model. The right panel shows a zoom to the latest ESPRESSO campaign. Middle panels: Combined RV time series of ESPRESSO and CARMENES with the best fit of the GP+2p model. The red line shows the best combined model, while the grey line shows the stellar activity component. Bottom panels: Residuals after the fit of the RV time series of ESPRESSO and CARMENES. The right panel shows the GLS periodogram of the residuals. The computation of the periodogram uses the offsets and the jitters estimated for model 2-Planets (Circ) in table B.1. — astro-ph.EP

We report the discovery and characterisation of two Earth-mass planets orbiting in the habitable zone of the nearby M-dwarf GJ~1002 based on the analysis of the radial-velocity (RV) time series from the ESPRESSO and CARMENES spectrographs.

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Alien planet found spiraling to its doom around an aging star
https://phys.org/news/2022-12-alien-pla ... aging.html
by Harvard-Smithsonian Center for Astrophysics

For the first time, astronomers have spotted an exoplanet whose orbit is decaying around an evolved, or older, host star. The stricken world appears destined to spiral closer and closer to its maturing star until collision and ultimate obliteration.

The discovery offers new insights into the long-winded process of planetary orbital decay by providing the first look at a system at this late stage of evolution.

Death-by-star is a fate thought to await many worlds and could be the Earth's ultimate adios billions of years from now as our Sun grows older.

"We've previously detected evidence for exoplanets inspiraling toward their stars, but we have never before seen such a planet around an evolved star," says Shreyas Vissapragada, a 51 Pegasi b Fellow at the Center for Astrophysics | Harvard & Smithsonian and lead author of a new study describing the results. "Theory predicts that evolved stars are very effective at sapping energy from their planets' orbits, and now we can test those theories with observations."

The findings were published Monday in The Astrophysical Journal Letters.

The ill-fated exoplanet is designated Kepler-1658b. As its name indicates, astronomers discovered the exoplanet with the Kepler space telescope, a pioneering planet-hunting mission that launched in 2009. Oddly enough, the world was the very first new exoplanet candidate Kepler ever observed. Yet it took nearly a decade to confirm the planet's existence, at which time the object entered Kepler's catalogue officially as the 1658th entry.

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Kepler-80 Revisited: Assessing the Participation of a Newly Discovered Planet in the Resonant Chain
https://arxiv.org/abs/2212.08695

In this paper, we consider the chain of resonances in the Kepler-80 system and evaluate the impact that the additional member of the resonant chain discovered by Shallue & Vanderburg (2018) has on the dynamics of the system and the physical parameters that can be recovered by a fit to the transit timing variations (TTVs). Ultimately, we calculate the mass of Kepler-80 g to be 0.8±0.3M⊕ when assuming all planets have zero eccentricity, and 1.0±0.3 M⊕ when relaxing that assumption. We show that the outer five planets are in successive three-body mean-motion resonances (MMRs). We assess the current state of two-body MMRs in the system and find that the planets do not appear to be in two-body MMRs. We find that while the existence of the additional member of the resonant chain does not significantly alter the character of the Kepler-80 three-body MMRs, it can alter the physical parameters derived from the TTVs, suggesting caution should be applied when drawing conclusions from TTVs for potentially incomplete systems. We also compare our results to those of MacDonald et al. (2021), who perform a similar analysis on the same system with a different method. Although the results of this work and MacDonald et al. (2021) show that different fit methodologies and underlying assumptions can result in different measured orbital parameters, the most secure conclusion is that which holds true across all lines of analysis: Kepler-80 contains a chain of planets in three-body MMRs but not in two-body MMRs.

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NASA Discovers Pair of Super-Earths With 1,000-Mile-Deep Oceans
Earth and Exoplanet Kepler-138 d Cross-Sections
https://scitechdaily.com/nasa-discovers ... ceans/amp/
NASA’s Hubble and Spitzer Find Two Exoplanets May Be Mostly Water

In the 1995 post-apocalyptic action film “Waterworld” Earth’s polar ice caps have completely melted, and the sea level has risen to over 5 miles, covering nearly all of the land. Astronomers have uncovered a pair of planets that are true “water worlds,” unlike any planet found in our solar system.

Slightly larger than Earth, they don’t have the density of rock. And yet, they are denser than the gas-giant outer planets orbiting our Sun. So, what are they made of? The best answer is that these exoplanets have global oceans at least 500 times deeper than the average depth of Earth’s oceans, which simply are a wet veneer on a rocky ball.

The soggy worlds orbit the red dwarf star Kepler-138, located 218 light-years away in the constellation Lyra. The planets were found in 2014 with NASA’s Kepler Space Observatory. Follow-up observations with the Spitzer and Hubble space telescopes found that the planets must be composed largely of water. The spectral signature of water wasn’t directly observed. But this conclusion is based on their density, which is calculated from comparing their size and mass.

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NASA's TESS discovers planetary system's second Earth-size world

https://phys.org/news/2023-01-nasa-tess ... world.html
by Jeanette Kazmierczak, NASA's Goddard Space Flight Center

Using data from NASA's Transiting Exoplanet Survey Satellite, scientists have identified an Earth-size world, called TOI 700 e, orbiting within the habitable zone of its star—the range of distances where liquid water could occur on a planet's surface. The world is 95% Earth's size and likely rocky.

Astronomers had previously discovered three planets in this system, called TOI 700 b, c, and d. Planet d also orbits in the habitable zone. But scientists needed an additional year of TESS observations to discover TOI 700 e.

"This is one of only a few systems with multiple, small, habitable-zone planets that we know of," said Emily Gilbert, a postdoctoral fellow at NASA's Jet Propulsion Laboratory in Southern California who led the work. "That makes the TOI 700 system an exciting prospect for additional follow up. Planet e is about 10% smaller than planet d, so the system also shows how additional TESS observations help us find smaller and smaller worlds."

Gilbert presented the result on behalf of her team at the 241st meeting of the American Astronomical Society in Seattle. A paper about the newly discovered planet was accepted by The Astrophysical Journal Letters.

TOI 700 is a small, cool M dwarf star located around 100 light-years away in the southern constellation Dorado. In 2020, Gilbert and others announced the discovery of the Earth-size, habitable-zone planet d, which is on a 37-day orbit, along with two other worlds.

The innermost planet, TOI 700 b, is about 90% Earth's size and orbits the star every 10 days. TOI 700 c is over 2.5 times bigger than Earth and completes an orbit every 16 days. The planets are probably tidally locked, which means they spin only once per orbit such that one side always faces the star, just as one side of the moon is always turned toward Earth.