Orbiting 53 light years away, an exoplanet which is earth-sized was discovered by NASA.
Another exoplanet, a warm mini-Neptune, was found in the same system by the Transiting Exoplanets Survey Satellite (TESS).
The star both planets orbit has the equivalent of 80% of our sun’s mass.Most of the exoplanets TESS will find are expected to have orbital periods of 10 days or less. The mini-Neptune was an exciting find for researchers because of its orbital period of 36 days. This made the discovery more challenging.
“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,” Teske said in a statement. One such tool, the Planet Finder Spectrograph on the Magellan II telescope 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 works using a technique called the radial velocity method, 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. So, it will be a very important part of further characterising the planets found by the TESS mission,” Teske added.
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.
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.
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.