February 20, 2022
Sunday, February 20, 2022
Our nearest neighbor star, Proxima Centauri, may now have three planets going around it. Well, it鈥檚 not a new planet, of course鈥攖he planets have been orbiting the red dwarf star for billions of years before humans ever looked up at the sky. It鈥檚 just that it hasn鈥檛 been until now that we have the capability of detecting it.
The discovery was announced in the . However, it is not a confirmed exoplanet. The team led by J.P. Faria notes that it is a 鈥渃andidate鈥� that needs to be confirmed by other independent teams in the . The initial step of peer-review is the 鈥渞efereeing鈥� of the paper to make sure the data and analysis are good enough to be published. The next step is other scientists not associated with the discovery group seeing if they can also detect the exoplanet or trying to find errors in the data or logic of the analysis.
The newly-discovered exoplanet candidate, 鈥淧roxima Centauri d鈥�, orbits closer to the star than the other two. At a distance of just 3 percent the distance between the sun and Earth, the new exoplanet takes just 5 days 3 hours to orbit the star. Proxima Centauri d can survive that close because Proxima Centauri is a faint that emits just 0.15% of the sun鈥檚 energy, so the of the exoplanet would be just 304 K (or 88 deg F) without an atmosphere. It would be , so the exoplanet鈥檚 surface temperature could be slightly less than the boiling point of water.
Because of its candidate status, the third exoplanet around Proxima Centauri is not listed in the but you can find it in the . In fact, the second exoplanet 鈥渃鈥� also but exoplanets found by looking at the wobble of a star (the 鈥溾��) usually take a bit longer to be independently confirmed.
The (radial velocity) method uses the fact that as the star gravitationally pulls on the exoplanet, the exoplanet also pulls on the star. The star, being so much more massive than the exoplanet, will have a much smaller motion than the exoplanet. The star will appear to wobble about the star-exoplanet system鈥檚 center-of-mass point while the exoplanet will have a much greater motion. Unfortunately, we can鈥檛 see the exoplanet directly, so we鈥檙e stuck using the star鈥檚 tiny motion to infer the existence of the exoplanet and its mass. The radial velocity method gives us a lower bound on its mass if we don鈥檛 know how much the orbit is tilted with respect to our line of sight. Proxima Centauri d鈥檚 mass is at least 0.26 times Earth鈥檚 mass (or about twice Mars鈥� mass).
was discovered several years ago using the radial velocity technique and it is well-confirmed. It orbits at 5 percent the distance between the sun and Earth and takes 11 days 4 hours to orbit Proxima Centauri. It has a mass of at least 1.27 Earths and its surface temperature would be on cool side at just 234 K (or -38 deg F) without an atmosphere. Atmospheres can significantly warm up a planet. Without an atmosphere, would be a chilly 254 K (-2 deg F) but the natural greenhouse effect warms us up to an average temperature of 288 K or 59 deg F. Some greenhouse effect is good but too much is not, as seen by our neighbor which has a surface temperature of 737 K (867 deg F) instead of being below the freezing point of water without an atmosphere.
Proxima Centauri c is the outermost exoplanet鈥攅xoplanet candidate. Also discovered via the radial velocity technique, its existence has not been solidified enough to make it to the NASA Exoplanet Archive. It orbits at a distance of 1.48 times Earth鈥檚 distance from the sun and it takes 1928 days (5.3 years) to orbit the star. Its minimum mass is 5.7 Earth masses and has a calculated average surface temperature of just 39 K (-389 deg F) or about as cold as Pluto. The James Webb Space Telescope will be trained on these worlds to see how dense are their atmospheres and the composition of them (assuming that 鈥渃鈥� and 鈥渄鈥� turn out to be real bona fide exoplanets). The will enable us to know whether or not liquid water could exist on the surface and maybe even life has changed the chemistry of the atmosphere like life has done on Earth.
Evening sky watchers still get to revel in the brilliant stars of Orion, Gemini, Taurus, and Canis Major. Early risers/night owls will have a treat on the pre-dawn morning of February 24 seeing a (one day past third quarter phase) right next to , the red heart of Scorpius. They鈥檒l be rising at about 2 a.m. and will comfortably fit together in the field of view of your binoculars. Three mornings later you鈥檒l see Venus, Mars, all within a fist鈥檚 width at arm鈥檚 length of each other. You might also be able to pick out Mercury to the left of the moon just before sunrise.
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Director of the William M Thomas Planetarium at 51今日大瓜
Author of the award-winning website
