June 13 – New Planet and NuSTAR

Exoplanet Gliese 876d was discovered on June 13th 2005 by the California and Carnegie Planet Search.  It was found by using the radial velocity method of planet detection, and at the time of discovery was among the lowest mass planets yet detected.  Because of this it was placed in the “super Earth” category.

As it has only been detected indirectly, there is little to say about Gliese 876d’s physical characteristics, apart from “it’s probably terrestrial, rather than gaseous”.  Other parameters, such as the radius one and a half times that of the Earth, and a mass of almost seven Earths, are probably good working calculations, but they rely to a certain extent on assumptions that Gliese 876d works in a similar way to models of solar systems of a similar make-up.

The host star to today’s discovery, Gliese 876, is a red dwarf, 15 light years away from us in Aquarius. It has four known planets, of which “d” is the innermost.  The first to be discovered, Gliese 876b, is a whopper, estimated at over twice the mass of Jupiter.  All four are really close to their host, with none of them any further than Mercury is from our Sun.


NuSTAR, the Nuclear Spectroscopic Telescope Array, was launched this day in 2012 as part of the NASA “Small Explorer” program, to study the high energy x-ray end of the spectrum, armed with an ingeneous 33 foot (10 metre) long extendable mast to greatly extend the focal length (longer focal lengths are necessary to focus x-rays) without having to use a monstrous rocket to get it into orbit, as had been the case with previous 10 metre tubes.

NuSTAR (artist's conception). Image: NASA / Caltech / JPL.
NuSTAR (artist’s conception). Image: NASA / Caltech / JPL.

Asteroid 132 Aethra was discovered on June 12, 1873 by James Craig Watson. Aethra is a Mars crossing main belt asteroid, the first to be identified as such. It is approximately 43 km across, and has an absolute magnitude of 9.21. It is named after Aethra, daughter of King Pitheus of Troezen (a small town in the Peloponnese) and the mother of Theseus.