New planet discoveries
An exoplanet or extrasolar planet is a planet that orbits a star other than the Sun. Nearly 2000 exoplanets have been discovered (1948 planets in 1232 planetary systems including 487 multiple planetary systems as of August 21, 2015). There are also rogue planets which do not orbit any star and which tend to be considered separately.
The Kepler space telescope has also detected a few thousand additional candidate planets to be further evaluated. So far there is at least one planet per star on average. https://en.wikipedia.org/wiki/Exoplanet – cite_note-Nature-20120111-9. About one in five Sun-like stars have an Earth-sized planet in the habitable zone, with the nearest around 12 light-years distance from Earth. Assuming 200 billion stars in the Milky Way, there would be 11 billion potentially habitable Earth-sized planets in the Milky Way, rising to 40 billion if red dwarfs are included. The rogue planets in the Milky Way possibly number in the trillions.
As of March 2014, the least massive planet known is PSR B1257+12 A, which is about twice the mass of the Moon. The most massive planet listed on the NASA Exoplanet Archive is DENIS-P J082303.1-491201 b, which is about 29 times the mass of Jupiter. However, according to most definitions of a planet, it is too massive to be a planet and may be a brown dwarf star instead. There are planets that are so near to their star that they take only a few hours to orbit and there are others so far away that they take thousands of years to orbit. Some are so far out that it is difficult to tell if they are gravitationally bound to the star. Almost all of the planets detected so far are within the Milky Way, but there have also been a few possible detections of extragalactic planets.
A super-Earth is an extrasolar planet with a mass higher than Earth’s, but substantially below the mass of the Solar System’s ice giants Uranus and Neptune. The term super-Earth refers only to the mass of the planet and does not imply anything about the surface conditions or habitability.
New exoplanet discoveries continue! On January 6, 2015, NASA announced the 1000th confirmed exoplanet discovered by the Kepler Space Telescope. Three of the newly confirmed exoplanets were found to orbit within habitable zones of their related stars: two of the three, Kepler-438b and Kepler-442b, are near-Earth-size and likely rocky; the third, Kepler-440b, is a super-Earth. On July 30, 2015, Astronomy & Astrophysics said they found a planetary system with three super-Earths orbiting a bright, dwarf star. The four-planet system, dubbed HD 219134, had been found 21 light years from Earth in the M-shaped northern hemisphere of constellation Cassiopeia, but it is not in the habitable zone of its star.
Our first SkyGazer meeting of the new season will be titled Minor Planet Update – Pluto, Ceres and Vesta by Shane Byrne of the University of Arizona’s Lunar and Planetary Laboratory. The meeting will be held at MountainView West Ballroom at 7:00 p.m. on October 11.