Mercury’s high density has been a longstanding puzzle in planetary science. Its density means that it must have a significantly higher iron abundance than Venus, Earth, Mars, or the asteroids, probably in the form of a large iron core. NASA’s MESSENGER mission has challenged many of the hypothesized ways to create an iron-rich Mercury; a new hypothesis is required.
Two years ago this month, I wrote my very first astrobite about the puzzlingly cloudy atmosphere of the outermost planet, HR 8799b; today I’m revisiting the system and looking at a recent paper which measured spectra of not just one planet, but the entire planetary system. This is the first comparative spectroscopic study of any multi-planet system (other than our own Solar System of course).
The census of planets for smaller stars—M dwarfs—is now basically complete. In this paper, Courtney Dressing and Dave Charbonneau use this M dwarf advantage to determine the occurrence rate of small planets around M dwarfs.
The holy grail for exoplanet science would be to find an inhabited planet. Not just habitable, but actually inhabited. But where are we most likely to find those planets? Only around Sun-like stars, or could life thrive around other types of stars? Could evolved stars like white dwarfs or neutron stars harbor life? Could brown dwarfs, the so-called failed stars, have inhabited planets?
Do planets form in place, or migrate?
How planets form is still a remarkably open question. We haven’t even figured out definitively whether planets formed in the places they are now, or formed in different places and then migrated to their present locations.
As a young astronomer, I’m excited to learn as much as I can about observing process. So when the chance to observe with a collaborator Sandy Leggett at Gemini North came up, I couldn’t pass it up! I spent a week in Hawaii learning about queue observing.
Astronomers don’t stop after discovering planets in systems near and far from our own solar system. The next big step is to characterize the planets. We want to understand what they’re made of, what their atmospheres look like, whether they have clouds, how massive they are, how old they are, etc. As it turns out characterizing exoplanets is really, really challenging for both observers and modelers. The challenges encountered are well illustrated by the saga of WASP-12b.
Astronomers have started trying to understand how to organize classes of exoplanets based on their physical characteristics. As it has turned out over the last ten years, exoplanets are considerably more complicated to classify than stars. The evolution of star is based (almost) exclusively on how massive it is at birth. Instead, this paper classifies hot exoplanets by their level of irradiation from their host star and their chemical composition.
It took homo sapiens hundreds of thousands of years on the planet to understand a fundamental, simple-sounding, question: how old is the Earth? The answer to this question has gone down in the history books as one of the most important geophysical and astrophysical discoveries of the past century. This paper, by Clair Patterson in 1956, is credited with providing the first accurate, measured age of the Earth.