An article published in “The Astronomical Journal” reports the discovery of the exoplanet LHS 1815b thanks to NASA’s TESS space telescope. A team of researchers led by Tianjun Gan of Tsinghua University in Beijing, China, confirmed the existence of that planet using various ground-based photometric, spectroscopic and photographic instruments. The conclusion is that its size is slightly higher than the Earth’s, but it’s much denser for a mass up to 8.7 times the Earth’s. The most unique feature is that it’s the first exoplanet discovered in the Milky Way’s so-called thick disk, one of the structures that make up about two thirds of disk galaxies.
Many spiral galaxies are made up of two disk-shaped structures that contain stars of different ages. The bottom image (NASA/JPL Caltech/R.Hurt/SSC) shows an illustration of which the Thin Disk and the Thick Disk are significant.
The so-called thin disk mainly contains relatively young stars while the thick disk in the Milky Way’s case contains about 20% of the stars and they’re the oldest ones. This division is still under discussion, also because there are various theories that try to explain this double structure, but so far no adequate evidence has been found that points towards a theory. The distribution of the star age has also been the subject of discussion due to the difficulty of matching data deriving from observations and theoretical predictions. A further mystery is that more than 4,000 exoplanets have now been discovered, but only a few in the thick disk.
The TESS (Transiting Exoplanet Survey Satellite) space telescope was launched on April 18, 2018. Its scientific mission’s initial period already offered interesting discoveries, but the exoplanet LHS 1815b is the first in the Milky Way’s thick disk, above the galactic plane, and that makes it intriguing. The data collected by TESS were verified using various ground-based telescopes that confirmed its existence.
Just over 97 light years away from Earth, the star LHS 1815 is a red dwarf shown in the top image captured using the Southern Astrophysical Research (SOAR) telescope (Courtesy Gan et al) with mass and size almost exactly half the Sun’s, which means that it’s much colder than the Sun with a surface temperature around 3,600 Kelvin. LHS 1815b is very close to its star, at a distance from it that is approximately 4% of the Earth’s distance from the Sun for a year that lasts less than 4 Earth days. This means that its surface is very hot and it’s unsuitable for hosting life forms similar to Earth’s.
The various detections of the exoplanet LHS 1815b carried out with the various instruments made it possible to obtain an estimate of its main characteristics. Its size is slightly higher than the Earth’s, but its mass is much higher given that there’s an estimate of 4.2±1.5 times the Earth’s but another gives an upper limit of 8.7 times the Earth’s. In short, it’s very dense even for a rocky planet, but further observations are needed to obtain a precise estimate.
There may already be other observations made by the TESS space telescope containing data about exoplanets in the thick disk. Follow-up research on LHS 1815b, also regarding its possible atmosphere, and the confirmation of more planets in the thick disk would allow to carry out studies on their evolution to understand if it’s different with respect to the planets in the thin disk, a new frontier in planetary astronomy.
