One of the fun new items was a story by Dr. James Davenport about how he helped convince NASA to use the Kepler space telescope to take a selfie of Earth.
“This is a personal story,” Davenport explained. “This is a story about an image that we asked NASA to take, and they were kind enough to take it.”
It took more than a year of cajoling, using the usual bureaucratic channels and also social media campaigns to get the shot.
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| Selfie from space: Earth as observed by Kepler in December. (Image: NASA) |
The Kepler telescope usually points away from Earth, but sometimes NASA moves the aim to look at a different part of the sky, and that’s when Earth can move through the scope’s field of view. This happened on December 10, 2017, and that’s when Kepler got this shot. Now, Kepler usually looks a dim objects that are far away—a typical exposure is about 30 minutes. This isn’t the best setup for taking a photo of Earth from about 94 million miles.
“We expected it to look like a bright mess,” Davenport said. “We were not disappointed.”
It’s a personal story for Davenport because he was doing an entirely different thesis project for his Ph.D. program when Kepler came on line. He was so excited about the hunt for exoplanets that he ditched his other thesis and started working with Kepler.
“It represented a huge turning point in my career,” he said.
Polarimetry
Back in September Kim Bott gave a talk about how she and other astronomers are using polarimetry to try to figure out if exoplanets are habitable or inhabited. Since then she’s done some actual modeling of Venus at various phases to see if polarimetry can tell us what we need to know.The short answer appears to be no, at least for right now. The instruments simply aren’t sensitive enough to detect the changes in light wiggle that might reveal a variety of indicators.
“It’s just a couple orders of magnitude,” Bott explained, “so something that we might be able to obtain within the next decade” as the technology improves.
Trappist 1
The planets around the star Trappist 1 have attracted a lot of interest since they were discovered beginning in 2015. There are seven planets in all orbiting this red dwarf star; they’re all roughly the size of Earth, and three of them orbit within the star’s habitable zone.
“There’s a very distinct pattern linking the orbital periods of all seven planets,” he said. Interestingly enough, this resonance and the gravitational influence the planets have on each other makes the transit times of the planets change from orbit to orbit.
“It’s just like when you’re at the bus stop here in Seattle,” he explained. “Sometimes the bus comes early, sometimes it’s on time, sometimes it’s late. Transits are the same way.”
This gives astronomers a lot of information about the system.
“By studying the transit time variations you can actually get the mass of the planets because you know how strong their gravity is,” Luger said. “Because of the geometry of the system we can get the radius of the planets—the size when it transits the star—and by doing some clever numerology and math we can figure out their mass. If you have the radius and the mass you actually have the density, so you have an idea what these planets are made of.”
It turns out that the Trappist planets mostly appear to be of lower density than Earth and Venus. This could mean that the planets have large amounts of water or large hydrogen atmospheres.
“These planets are going to be studied a ton in the next decade to figure out if in fact they are habitable,” Luger said.
Astronomy on Tap Seattle co-founder Brett Morris noted that much future study of exoplanets was to have been done by the James Webb Space Telescope, but the recent decision to delay the launch of that instrument has been disappointing to many.
“That affected some people a lot,” Morris said. “Some of those people were me!”
When the announcement that the launch would be pushed out to 2020 was made last month, Morris and others were coming up on what was an April 6 deadline to propose observing targets for the Webb.
“We were all working really hard because this telescope is super cool and it’s going to be the one that’s going to tell us if these planets are actually habitable and what’s going on in their atmospheres,” Morris noted. “Then the rug got pulled out from under us.”
R-process is better than your process
Back in July Trevor Dorn-Wallenstein told the AoT crowd how the universe makes beer for us. Last month he explained how heavier elements are made, and how we now know that theory to be true.Dorn-Wallenstein explained how elements are made within stars. Typically, when neutrons collide with protons, they are captured. Nature stabilizes this through a process known as beta decay; the neutron just turns into a proton. This causes the release of an electron and a neutrino, or maybe an anti-neutrino.
“The jury is still out on whether neutrinos are the same as anti-neutrinos,” Dorn-Wallenstein observed. In any case these particles just go away.
“What we’ve really done here is we’ve converted one of those neutrons into a proton, and in doing so we’ve made a whole new element,” Dorn-Wallenstein said. “We’ve gone from hydrogen to helium, though both are unstable and have oddball numbers of neutrons.”
This happens slowly—that’s why it’s called the s-process. It occurs in low-mass stars, which can make strontium, barium, and lead.
Then there’s the r-process, which is rapid. In this process neutrons get bombarded onto atomic nuclei so quickly that beta decay can’t happen, and you get ridiculously unstable nuclei. Eventually neutron capture either slows, or it becomes so unstable that beta decay happens all at once, and BAM, you’re making silver, gold, platinum, and other heavier elements.
Essentially to do this you need three big explosions. First you need two supernovae to leave behind a pair of neutron stars. Then the neutron stars need to merge. Their collision is called a kilonova.
“There’s a lot of free neutrons around, and maybe those free neutrons are created rapidly enough that the r-process occurs,” Dorn-Wallenstein said. To confirm this you’d need to see evidence of a neutron star collision, a gamma-ray burst from the event, and follow up to make sure r-process elements were actually being formed. That’s exactly what happened when LIGO detected gravitational waves from a neutron star merger back in August.
“We found evidence that r-process elements were being formed and it confirmed that neutron star mergers were the dominant sites of the r-process,” Dorn-Wallenstein concluded.
Exoplanet instruments
Back in August Lupita Tovar did a talk about LUVOIR and SAMURAI and how they will help us map exoplanets. Her latest interest is the Transiting Exoplanet Survey Satellite—TESS—which launched April 18. Its primary mission is to search for Earths and super-Earths. While Kepler looked at a relatively small swath of sky, TESS will scan about 80 percent of the sky and observe some 200,000 stars.“You can imagine how many more things we’re going to be finding,” Tovar marveled. TESS will look at brighter stars than Kepler was able to observe, and will be a constant source of data. It will send back full-frame images every half hour or so, and about 200,000 smaller “postage stamp” images every two minutes.
“What that translates to is a whole lot of data that’s going to be coming down from this telescope,” Tovar said. “You’re going to get a lot of planets—planets everywhere!”
There could be as many as 20,000 new ones; Tovar said many will likely be gas giants, which are easier to spot.
SPAMS a lot
UW student Aislynn Wallach is involved in a project called The Search for Planets Around post-Main Sequence Stars—SPAMSS.The question is what becomes of planets like Earth when their host stars become red giants.
“They blow up to a larger size, much like a marshmallow in a microwave,” Wallach said. After that the stars become white dwarfs. The prospects for the close-in planets aren’t good.
“Anything inside (the expanded red giant) will probably be disintegrated,” Wallach noted. “That’s what we’re trying to find—these broken up planets around stars like the Sun.”
The approach is to look at the spectra of white dwarf stars. If we spot heavier elements in those spectra, the elements will have come from ripped-up planets. If those materials were part of the star, they would sink quickly from its surface.
For her search Wallach has been using the ARCSAT (Astrophysical Research Consortium Small Aperture Telescope) at the Apache Point observatory in New Mexico. Results of her search so far: nothing.
“Nothing is still a result!” She laughs. The search continues.
The beautiful music of the universe
An interesting new approach to data is to turn it into sound. Locke Patton is doing this with the brightness of supernovae. Brighter data points are assigned higher musical pitches. The process is called sonification.“We don’t just look at it, we listen to it,” said Patton of the data.
Sadly, his recording of a supernova sound didn’t play—a rare technical glitch at Astronomy on Tap Seattle. He sang it. Sort of! You can hear a recording here.
