Yesterday’s big afternoon press conference was all about exoplanets. The scientists took us on a tour de force of planet related press releases that went from little M stars and their tiny habitable zone, to a new press release on 28 planets, to planets found around sub-giant stars that were A-stars when they were on the main sequence. The catch was, while none of these stories had previously had related press releases, many of them (but not all) had related published papers or published pre-prints in the arXiv pre-print sever.
Living with a Red Dwarf: Dr. Ed Guinan (Villanova University) presented a clean bit of research that demonstrated that M dwarf stars may be capable of calmly illuminating their planets for 40 billion plus years, but before they do that they like to wreck havoc with X-ray and far ultraviolet emissions. When first born, these stars rotate very quickly (periods of hours), and then gradually slow to longer periods (measured in 10s of days). When the star is rotating faster, it has a stronger magnetic field, and also has stronger and more frequent coronal mass ejections. These events release vast amounts of high energy radiation that will destroy and blast off the atmospheres of any planets without a magnetic field. These high energy blasts continue for over 1 billion years. Unfortunately, any planet in the habitable zone of an M dwarf will become tidally locked to the star in less then 0.5 billion years, and thus will rotate only once per orbit. With this slow of a rotation, the planet will lose its magnetic field. This implies that any planet within the habitable zone of an M dwarf will be made uninhabitable.
28 planets announced: The second announcement was just a press release stating that there are 28 more planets on the exoplanet.org website than there were when they last had a press release. All but 2 of 3 of these planets had already been published, and coverage has already appeared in much of the media.
A-list planets: In the final presentation, Dr. John Asher Johnson (University of California, Berkeley) showed that it is possible to find planets around stars that were A-stars on the main sequence. These planets also helped to define a relationship that shows the frequency of planets being found around stars is directly related to their mass, with larger stars having planets more often. Oddly, the locations of the planets around these “retired A-stars” don’t follow the same distributions seen in smaller stars. For some unknown reason, planets around former A-stars avoid the inner solar system, and are found predominately outside of 0.8AU.
This piece of work showed an interesting way of diagnosing planetary populations in eone type of star using surrogate populations. We want to know how many main sequance A-type stars – stars hotter and more massive than the Sun – have planets. We can’t with current technology measure that directly. A stars are so hot that they have very few spectral lines (most of the atoms are completely ionized) and rotate very quickly, with broadens the spectral lines so much that doppler shifts caused by planets can’t be measured. When these stars evolve off the main sequence and begin burning hydrogen in a shell around their helium core, they expand, cool, and rotate slower. This means planets can be looked for using doppler shifts. We just have to assume the number and physical locations of the planets don’t change too much during the evolution, and this is a pretty big assumption.
From the Audience: It was this last bit that lead to one of the most fascinating exchanges of the press conference. During the questions session, several people asked “So what is new about this?” and then someone else clarified “No, what is new and hasn’t been in a journal article or pre-print.” This lead to a fascinating moment in which we, the journal reading press, got to educate a small group of scientists about how much we read what they are doing. In what was the sub-news of the day, it became very clear that the science that is reported isn’t limited to what comes out the press release engines, but rather we the press are, as a community, reading the journals to look for the next big thing, and reporting the results of peer-review without worrying if some press officer has or has not sent us pre-digested content for mass distribution. In that moment, I was really proud of the group of people I get to work with in the AAS press room.
A black hole press conference is about to happen, and I’ll have more on that in a little bit.