TESS Sees Some Planets

[lpetrich]

Or more precisely, some planets have been discovered from transits observed by that satellite. [NASA Exoplanet Archive](https://exoplanetarchive.ipac.caltech.edu/) notes 9 confirmed planets and 482 candidate planets in TESS's data.

Data flows from NASA's TESS Mission, leads to discovery of Saturn-sized planet -- ScienceDaily is about another one. The planet orbits star TOI-197 ("TESS Object of Interest"), and TESS's observations have enabled the discovery of both the planet and some of the star's interior features. The latter is "starquakes", and research into them is "asteroseismology". Some of the articles that I found on this discovery had mixed up the planet transits and the starquake observations, and I was glad to discover that that ScienceDaily did not mix the two up. Once this planet was discovered, its star was observed with a high-resolution spectroscope, and that enabled radial-velocity measurements.

The star has a mass of 1.2 solar masses and a radius of 2.9 solar radii. It is around 5 billion years old, and it has started to move off the main sequence to become a red giant.

The planet has 60 Earth masses and 9 Earth radii, with a density of about 0.4 g/cm^3, a little less than Saturn's, 0.7 g/cm^3. It orbits at about 0.12 AU with a period of 14.3 (Earth) days. It received about 343 times as much light per unit area as the Earth does, implying an equilibrium temperature of about 1300 K.

Turning to the star's oscillations, the most prominent ones are around frequency of 430 microhertz, or an oscillation period of 39 minutes. Their combined amplitude is about 20 parts per million.

The system's distance is 95 parsecs or 310 light years.

Data flows from NASA’s TESS Mission, leads to discovery of Saturn-sized planet • News Service • Iowa State University
[1901.01643] A Hot Saturn Orbiting An Oscillating Late Subgiant Discovered by TESS

 

[lpetrich]

NASA’s TESS spacecraft finds its first Earth-sized exoplanet noting TESS Delivers Its First Earth-sized Planet and a Warm Sub-Neptune - IOPscience

Their star, HD 21749, is a K4.5 main-sequence star about 16 parsecs / 52 light-years away. Its apparent visual magnitude is 8.1, and its absolute visual magnitude 7.1. I estimate its mass to be 0.7 solar masses and its total luminosity to be 0.16 solar luminosities ( Main sequence). The two planets:

HD 21749b (TOI 186.01): size 2.61 Re, mass 22.7 Me, period 36d, distance 0.19 AU, equil. temp. 403 K - 130 C
Avg. density = 7.0 g/cm^3. This suggests a mostly rocky planet, but a table at Li Zeng's Homepage suggests rock with 20% by mass water.

HD 21749c (TOI 186.02): size 0.892 Re, period 7.8d, distance 0.068 AU, equil. temp. 674 K = 401 C

The equilibrium temperature for 1 solar luminosity at 1 AU is 278 K, 5 C. The Earth's average temperature is 15 C, due to s small greenhouse effect.

 

[lpetrich]

Discovery! 3rd Planet Found in Two-Star 'Tatooine' Star System | Space noting Discovery of a Third Transiting Planet in the Kepler-47 Circumbinary System - IOPscience It was discovered with the Kepler data, despite that spacecraft not operating anymore.

Kepler-47 is a roughly 3.5-billion-year-old system located 3,340 light-years from Earth. One of its stars is quite sunlike, but the other is considerably smaller, harboring just one-third the mass of our sun. The two stars orbit their common center of mass once every 7.45 Earth days.

...
That planet is the newly announced Kepler-47d, which is about 7 times bigger than Earth. That's considerably larger than Kepler-47b and c, which are 3.1 and 4.7 times wider than our planet, respectively.

Kepler-47b and c complete one lap around the circumbinary system every 49 and 303 Earth days, respectively. Kepler-47d's orbital period is 187 Earth days, which means it's the middle planet. And that came as a surprise; the team thought any additional planets in the system would probably be exterior to Kepler-47c.

...
But it's unusual for relatively temperate planets such as the Kepler-47 trio, whose average temperatures are thought to be about minus 26 degrees Fahrenheit (minus 32 degrees Celsius; Kepler-47c), 50 F (10 C; Kepler-47d) and 336 F (150 C; Kepler-47b).