How hot is too hot? You don't want to go here
By Amanda Jermyn



Welcome to the weird and wondrous world of 55 Cancri e, an exoplanet 40 light years from Earth in our Milky Way galaxy. Discovered in 2004, it was initially thought to be a water world. Later, as I reported back in 2013, it was proclaimed a “diamond planet,” composed mainly of carbon, which under extreme pressure forms diamonds. New discoveries by an international team of researchers led by Brice-Olivier Demory of Cambridge University and published in the journal Nature reveal an even stranger world.

The planet, now also called Janssen, in honor of Dutch telescope pioneer Zacharias Janssen, is the closest of five planets orbiting a Sun-like star. With a radius twice that of Earth and a mass eight times greater, it is considered a super-Earth, a term used to describe extra-solar planets with masses between one and ten times that of Earth. The planet orbits extraordinarily fast, with its year lasting only 18 hours. Because it is so close to its star, about 26 times closer than Mercury is to our Sun, it is tidally locked by gravity, just as our moon is to the Earth. This means that the same side of the planet is always facing its star. And because of its proximity to its star, it is scorchingly hot.

How hot has recently been discovered by Demory and his team, using infrared sensors on NASA’s Spitzer Space Telescope to create a temperature map of the planet. What they found was a world of extremes, with hot nights and even much hotter days. The day side, always facing the star, is about 4,400 degrees Fahrenheit and the night side is about 2,060 degrees Fahrenheit, a whopping difference of 2,340 degrees. This indicates that heat is not being distributed around the planet very well. One explanation is that the planet lacks a large atmosphere and winds to transport heat. This would make sense, as the planet is so close to its star that you would expect any of its early atmosphere to have vaporized. Another possibility is that it has molten lava on the day side but hardened lava on the night side, with the latter being unable to transport heat. A further enigma is that the Spitzer data shows the hottest spot not at the point closest to the star where one would expect it to be but rather half way between this point and the night side, suggesting flowing lava may be responsible.

While poor heat distribution around the planet and its proximity to its star suggest that 55 Cancri e should not have much of an atmosphere, a recent study appearing in the Astrophysical Journal reports that the planet does indeed have an atmosphere. Using data from the Hubble Space Telescope, Angelos Tsiaras of University College, London and his team found an atmosphere rich in hydrogen and helium, and potentially containing hydrogen cyanide. If further research confirms the presence of hydrogen cyanide, this would indicate a carbon-rich atmosphere and support the idea of a diamond planet, as previously suspected.

With so many anomalies still to be resolved, astronomers are now pinning their hopes on the James Webb Space Telescope, scheduled to launch in October 2018, to help unravel some of the mysteries of this exotic world.

Join the Springfield Stars Club on Tuesday, May 24th at 7:00pm at the Springfield Science Museum for a talk by Dr. Jason Young on “Low Surface Brightness Galaxies: The Life Story of the Milky Way’s Dark Counterparts.” Dr. Young is a Visiting Professor of Astronomy at Amherst College. His research focuses on star formation in galaxies similar to our own Milky Way but which produce stars at a much slower rate. For reasons not fully understood, these faint galaxies have retained up to 90% of their original gas instead of producing stars. Dr. Young and his team use space and ground based telescopes to discover why these galaxies produce stars so slowly, and through comparison, why galaxies like our own Milky Way have been so successful at producing stars. Refreshments will be served, and the public is welcome. The meeting is free of charge for members, with a suggested donation of $2 per non-member.