With the large number of exoplanets that we have discovered today (more than 4,000), finding one with a different particularity deserves to be highlighted. Its name is LHS 1815b and, although its scientific name may not tell you anything, it is an exoplanet that lives outside the disk of our galaxy. Its mass is 8.7 Earths and it takes only 3.8 days to complete one orbit of its star, from which it is 0.0404 astronomical units away.
While most stars that have planets orbit the Milky Way in the plane of the disk (which is what all these exoplanets have in common), the orbit of this planet’s host star pulls it out of this galactic plane, moving it high above the galaxy and far below it over time , giving it a beautifully interesting view of the Milky Way. And making it particularly fascinating.
We say that our galaxy has a flat disk, but it is somewhat more complicated: it has a thin one and a thicker one. One with younger stars and one with older stars and poorer in heavy elements. The thinnest disk in the Milky Way, a few hundred light-years thick, is where most of the stars and all the gas are found . But there is a more swollen disk around it, much thicker (about 20,000 light years thick) and sparsely populated with stars; The few stars that remain there are almost all 10 billion years old and, according to a recent study, they could have ended up here through a collision with another galaxy. Their orbits pass through the thinner disk to the thicker disk, up and down the galactic plane. But very few stars reach this far from the galactic plane.
How was the exoplanet discovered?
NASA’s TESS (Transiting Exoplanet Survey Satellite ) space telescope for hunting planets was responsible for the discovery: an exoplanet orbiting a star that plunges up to 5,870 light-years above the galactic plane. This mission is responsible for examining the entire sky, looking for planets around the brightest stars, hence it is normal to locate planets within our galactic neighborhood.
Its star, LHS 1815, is a red dwarf, a dim bulb of a star half the size and mass of the Sun, located about 97 light-years away in the constellation Pictor or the Painter’s Easel. It is dim and radiating only 4% of the Sun’s light.
Scientists took very precise spectra of the star over time to determine the planet’s mass: as the star orbits, the planet’s gravity pulls on the star; thus, while the planet draws a large circle, the star performs a small one. That creates a Doppler effect in the star’s light, which can be measured in the spectra.
The planet, discovered by the transit method, circles the star, passing directly in front of it once per orbit. It blocks a small amount of light from the star, creating a decrease in its brightness, precisely what its presence reveals. From the amount of light blocked, astronomers were able to measure the size of the planet. According to the data received, it is probably a rocky and incredibly dense world, because within that sphere of a similar size to our Earth (that is, 1,088 times the size of the Earth) it accumulates up to 8.7 times its mass.
Almost four times denser than Earth. Is it possible that it was a much larger planet in the past? We do not know this extreme. What is exciting is that this is the first thick disk planet to be found in the TESS data, and hopefully many more will be detected. If we can find them, they could also be studied to find out how exoplanets evolve in different parts of the galaxy.
We leave a question in the air. Could this exoplanet have formed in another galaxy?
Referencia: LHS 1815b: The First Thick-Disk Planet Detected By TESS Tianjun Gan, Avi Shporer, John H. Livingston, Karen A. Collins, Shude Mao, Alessandro A. Trani, Davide Gandolfi, Teruyuki Hirano, Rafael Luque, Keivan G. Stassun, Carl Ziegler, Steve B. Howell, Coel Hellier, Jonathan M. Irwin, Jennifer G. Winters, David R. Anderson, César Briceño, Nicholas Law, Andrew W. Mann, Xavier Bonfils, Nicola Astudillo-Defru, Eric L. N. Jensen, Guillem Anglada-Escudé, George R. Ricker, Roland Vanderspek, David W. Latham, Sara Seager, Joshua N. Winn, Jon M. Jenkins, Gabor Furesz, Natalia M. Guerrero, Elisa Quintana, Joseph D. Twicken, Douglas A. Caldwell, Peter Tenenbaum, Chelsea X. Huang, Pamela Rowden, Bárbara Rojas-Ayala. Accepted for publication in AJ 2020 DOI 10.3847/1538-3881/ab775a
