Julian Date: 2459054.16
2019-2020: CLXXXIII
THE DAILY ASTRONOMER
Thursday, July 23, 2020
Remote Planetarium 70: Exo-Planets Q/A
Today we conclude our series about exo-planets with a brief Q/A. If you have any questions not addressed in this article, please send them to me!
Where is the nearest exo-planet?
The nearest exo-planet is as close as the closest star, Proxima Centauri. Astronomers have found two planets in orbit around Proxima, the red dwarf star that is part of the Alpha Centauri system. Proxima Centauri is 4.2 light years away from Earth. These planets are known as Proxima Centauri b and Proxima Centauri c. The second of these planets is seven times more massive than Earth and revolves well outside the habitable zone. The first planet's mass is only slightly greater than that of our home planet and is well within that zone. Because Proxima Centauri is a red dwarf star, its habitable zone is very close to it. Proxima Centauri b's mean distance from its parent star is only 3.7 million miles and it completes one orbit every 11.2 days. While this planet could harbor life as it is both terrestrial and within the habitable zone, it is also subjected to strong stellar winds: 2000 times more powerful than the solar winds we experience on Earth. Such a high bombardment of radiation might preclude life's development on Proxima Centauri b.
Is it true that astronomers have found an exo-planet in the Andromeda Galaxy?
Possibly. PA-99-N2 is a microlensing event observed in the Andromeda Galaxy, 2.2 million light years from the Milky Way. It is possible that a star within the galaxy micro lensed either a smaller star or a planet. Micro lensing occurs when a massive body in front of a luminous one causes the light to bend gravitationally around it, by which it produces two images. The identity of the microlensing body remains a matter of contention. If confirmed, that object would be the most distant exo-planet yet discovered.
Have any exoplanets been directly imaged?
Yes, quite a few of them, actually. If the planet revolves at a sufficient distance away from its parent star, it can be resolved, provided that the star is also relatively close to us. As of now, about two dozen exo-planets have been discovered through direct imaging.* With one exception (CVSO 30 c), these directly imaged exo planets are located less than 1000 light years from Earth.
Time lapse images of Beta Pictoris b, a planet around Beta Pictoris.
Are there many planets around double, triple and even quadruple star systems?
So many people want a Tatooine sky: two or more suns in view! Fortunately, there might be quite a few. According to a 2019 survey, within 1600 light years of the Sun there could be 176 binary stars, 27 triples and at least one quadruple star that contains planets. The types of orbits will vary however. For instance, astronomers recognize "P type," "S type" and "T type" orbits within a binary system. A planet moving along a S-type orbit revolves around only one star within the system. A planet in a P-type orbit revolves around both.
In a T-type orbit, the planet would be around one of the two main L points along the secondary star's orbit. Any system consisting of two gravitationally bound bodies will also contain five L points (Lagrangian equilibrium stability points.) Three of these points are located along a straight line connecting the bodies. Two others are along the secondary body's orbit, one sixty degrees ahead, the other sixty degrees behind. These are the two most stable L points and one could find planets within their vicinity. See graphic below.
*Some of these directly imaged planets might instead be brown dwarfs, gaseous bodies that never became massive enough to ignite the core thermonuclear fusion reactions that power stars.
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SKYWATCHING TIP OF THE DAY: Mercury in the morning
Mercury reached greatest elongation on July 22nd. At that time, the first world appeared 20 degrees from the Sun in the pre-dawn eastern sky. Try to find Mercury throughout the remainder of this week. Venture out around 4:30 a.m. and find an unobstructed eastern horizon.
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