The constellation Cancer, visible in the west just after sunset is not a particularly prominent constellation, but it is host to a fairly well known star. 55 Cancri has made the news a fair bit as a more and more planets have been discovered around it. Also known as rho 1 Cancri, it is a fairly dim (but just about visible) star in the upper right claw of Cancer.
The star is a binary system – 55 Cancri A is an unusual metal rich star, cooler and dimmer than our own sun, while companion 55 Cancri B is a much dimmer red dwarf. 5 planets have been discovered orbiting the brighter star; they are lettered b, c, d, e and f in order of their discovery. The one closest to the star, e, was discovered in 2004 and is believed to be about twice the size of the Earth in diameter and perhaps 8 times as massive. It is very close to its star, orbiting every 18 hours and it transits across the face of the star, making it a great target for exoplanet observers.
Image credit: NASA/JPL-Caltech
Very recently, using the Spitzer space telescope, a team of scientists have detected light coming from the planet itself. Before this, telescopes would have looked for the light of a star to be affected as a planet moved its face, but now it is possible to look at the loss of light as a planet passes behind a star. Since Spitzer works in the infrared, it has detected the heat from the planet, revealing a hot dark planet. Closer to its star than Mercury is to the Sun, on 55 Cancri e the sun-facing side is more than 2,000 Kelvin. This fits with the idea that this is a water world: a rocky core surrounded by a layer of water in a “supercritical” state where it is both liquid and gas; topped by a blanket of steam. This planet is the smallest planet that has been studied in this way – before this only Jupiter sized gas giants (or larger) were detectable, but some technical fitzing with the telescope has improved its ability to point at targets.
This planet could not support life, but planet f, likely a gas giant, orbits the star within its habitable zone, so perhaps one of its possible moons might? The team behind Cosmic Call 2 sent a message to the star system back in 2003. Using a radio dish in the Crimea, a host of previously developed messages and some new content were beamed out to space. In May 2044 the system will be receiving data including the song “Starman” by David Bowie, music and images of the rock band KFT from Hungary, all the files of the website HellotoETI, created by the late Allen Tough, a Canadian futurist and even the text of a resolution passed by the New Mexico state legislature in 2003 designating the second Thursday (edited! I thought it was a Tuesday originally) in February as “Extraterrestrial Culture Day” in New Mexico.
This episode of “What is the Stars?” was first broadcast during the week of May 21, 2012. Listen live on RTÉ’s lyricfm on Mondays and Fridays at 22:45.
