Category Archives: astronomy

Waffles and big data in the universe

Waffles and big data were on the menu at the most recent gathering of Astronomy on Tap Seattle at Peddler Brewing Company in Ballard.

Leah Fulmer

Fulmer at work. Photo: Astronomy on Tap Seattle

Leah Fulmer, who is working at the University of Washington on her Ph.D. in astronomical data science, gave a talk titled, “Data-Driven Astronomy in the 2020s and Beyond.” Fulmer explained that we’re in the midst of a “data tsunami” that’s been growing over the last three decades of astronomical surveys.

Back in the 1990s the Palomar Digital Sky Survey and the Two Micron All-Sky Survey each collected about a terabyte of data. That’s a trillion bytes; 1012 bytes. Enough to fill a thousand one-gigabyte smartphones.

The 2000s brought the Sloan Digital Sky Survey (SDSS) and the Galaxy Evolution Explorer. These collected in the tens of terabytes of data. In the 2010s Pan-STARRS collected a petabyte of data; a quadrillion bytes.

In the future this astronomical growth in data collection will continue. The Large Synoptic Survey Telescope (LSST) under construction in Chile will survey the entire night sky every few nights for ten years. It will ultimately collect an astounding 500 petabytes of data—that’s 20 terabytes every single night.

“SDSS had a total data collection of 40 terabytes,” Fulmer pointed out. “We’re going to have one SDSS every two nights in the 2020s. This is a big freaking deal.”

On top of the data, Fulmer noted that the LSST will alert its network when it finds something interesting. Given the amount of data, Fulmer said there will be ten million alerts every night, or about 232 every second.

“This is overwhelming; this is a data tsunami,” she said. “With this sort of data collection astronomers cannot do our science in the way we have up until this point.”

A new way to look at data

Up until recently astronomers would apply for telescope time, make their observations, take the data home, and analyze it. That won’t work in the era of big data for a couple of reasons. First, you can’t jam that much data onto your laptop. Second, there just aren’t enough astronomers to sort through data on objects one by one. As you might guess, we need the help of computers.

“Specifically, we need the help of machine learning,” Fulmer said. This can be both “supervised” and “unsupervised” learning. Astronomers can identify objects by their light curves, and the computers can be taught what those are. That’s supervised. In unsupervised learning, the computers can go out on their own and sort various observations into categories with similar characteristics, and we can figure out what’s in each category.

Once you figure that out, a data broker like ANTARES (the Arizona-NOAO Temporal Analysis and Response to Events System, and yes, astronomers still rule at acronyms) can let the right people know about discoveries in a timely manner.

Fulmer said it’s interesting that ANTARES will never look at the sky, just at data, and that many future astronomers may never visit a telescope, just analyze the data. Different fields can learn from each other about how to process all of this information.

Fulmer finds the era of big data exciting.

“It’s not just data-driven astronomy, it’s data-driven everything,” she said.

Astronomy with your breakfast

N. Nicole Sanchez is working on her Ph.D. in astronomy at the UW, and her research interest is in spiral galaxies like our own Milky Way and how they evolve. This, naturally, led her to think of galaxies as waffles. Thus the title of her talk, “Black Holes, Gas, and Waffles.”

Spiral galaxies form into disks, she explained, and a waffle is a disk. The galaxies have a central bulge, represented on the waffle by a big pat of butter. Marshmallows, suspended by toothpicks, represent globular clusters of stars. Red and blue sprinkles represent old red stars and young blue ones. You just have to imagine the supermassive black hole at the center of the waffle. It may be massive, but it’s super small compared to the size of the waffle.

Sanchez came up with the idea for this model while teaching at the UW in the “Protostars” summer science camp for middle school girls the last couple of years. In the waffle model, syrup represents the gas in the galaxy.

“That’s what you’re making your stars out of, so there’s going to be a lot in your disk,” Sanchez said.

In fact, her faculty advisors got wind of the waffle model and said it would need A LOT of syrup, which led to the hilarious twitter thread below. Click on it to see the academic discussion.

Sanchez admitted that her waffle galaxy may be “a bit too simplified” as a model. But the syrup is important.

“There’s actually tons of gas around really all galaxies, in what’s called the circumgalactic medium,” Sanchez said. The gas is important to the evolution of a galaxy. It feeds the black hole and helps  form stars.

Sanchez studies galaxies by using cosmological hydrodynamic simulations.

“I put a bunch of particles in a box, turn on gravity, and let time happen,” she laughed. After running a simulation she looks for a galaxy similar to the Milky Way, and examines interactions between the galaxy’s supermassive black hole and the circumgalactic medium.

“The supermassive black hole is actually really vital to the evolution of the CGM because it’s moving all of this metal that’s being created in the hearts of stars in the disk of the galaxy and it’s propagating them out into the CGM,” Sanchez explained. Without a supermassive black hole, the circumgalactic medium would not look like what astronomers have observed.

Pass the syrup.

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Exploring the solar system with Emily Lakdawalla

Emily Lakdawalla gushes with enthusiasm about the cool things to see and learn in our solar system, and for her that would be reason enough to explore those places.

“I’m just curious,” she told the Rose City Astronomers at their most recent meeting in Portland. “I like to see the new places, I like to see the planets. I think it’s awfully fun, but that’s not a good reason to make somebody else pay for it.”

Lakdawalla

Emily Lakdawalla (Isabel Lawrence/Planetary Society)

Lakdawalla, senior editor and planetary evangelist for the Planetary Society, said the public policy reasons for exploration are to answer the questions of how we got here and whether we’re alone in the universe. We need to find those answers off-planet.

“Earth is a wonderful planet to live on!” she said. “It’s my favorite planet; it’s temperate, it’s a very comfortable place to live. It’s also a terrible place to try to answer these questions from a planetary science point of view.”

That, she says, is because Earth is dynamic. Forces like weather and volcanism and even life and evolution change things and mess up the ancient evidence about how things were before. We need to go to space to find territory in a more undisturbed state.

After the first wave of planetary exploration, with Viking, Mariner, and the like, enthusiasm and political will and funding for planetary exploration waned. Lakdawalla explained that the Planetary Society was founded in 1980 to be an advocate for finding the answers. We’re now enjoying a second wave of exploration.

“Since the end of the second millennium, we’ve had this amazing expansion of robotic space explorers all over the solar system,” Lakdawalla said. She talked about many of them, with a particular emphasis on Mars. This is squarely within her bailiwick, as she is the author of the book The Design and Engineering of Curiosity: How the Mars Rover Performs Its Job (Springer Praxis Books, 2018).

She explained how a series of Mars missions followed the water. Mars Global Surveyor made a map. Mars Odyssey detected evidence of hydrogen by analyzing neutron movement, and hydrogen could mean water. Phoenix went to look for water and found ice. Mars Express found places where there’s clay, evidence of water, in many places. Curiosity went to one of those places.

“Curiosity has found environments on Mars that are unequivocally habitable,” Lakdawalla said. “Curiosity is not capable of looking for fossil evidence of microbial life on Mars. It doesn’t have the instruments.”

While Curiosity continues its mission, Lakdawalla said we’ve pretty well exhausted this particular line of research.

“We have found that, yes, Mars could have originated life in the past, but we can’t tell you if there was life there or not,” she said. That question will be up to the next line of rovers, such as the ESA’s ExoMars and NASA’s Mars 2020.

Lakdawalla spent some time on the outer solar system, particularly the life possibilities on the jovian moons Ganymede and Europa and Saturnian moons Titan and Enceladus. She noted that on Titan the temperature is such that methane could exist on the surface in liquid, gas, or solid forms, much as water can exist on Earth. The Huygens probe found round rocks on Titan, a significant discovery for a geologist.

“We have a river, except it’s a bizarro river,” Lakdawalla said. “Those rocks are made of water ice, and the river they were tumbled in was a methane river. It’s so familiar and so completely bizarre.” She said it’s hard to say if life could exist in that strange environment. Another reason for further exploration!

Lakdawalla said she’d love to see a mission soon to either Uranus or Neptune.

“They don’t get enough respect,” she said. “I think they’re awesome worlds.” But remembering her statement that coolness alone isn’t enough of a reason for the trip, she noted that the ice worlds are at an intermediate size between the gas giants and the terrestrial planets.

“Most of the exoplanets that we have discovered in the last 30 years have been of this size,” Lakdawalla noted. “We’ve never studied up-close the ones in our own solar system except for one Voyager 2 fly-by. We don’t understand these worlds very well at all, so how are we going to understand the rest of the universe and all of these other planets orbiting all of these other stars?”

Lakdawalla concluded that it’s a great time to be in the planetary exploration business.

“We’re doing it for a reason; we’re trying to understand how we got here, whether we’re the only life in the solar system,” she said. “It’s just a wonderful field of study.”

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Astro Biz: Orion apartments

Orion apartmentsMany businesses, products, and places have names rooted in space and astronomy. We’re featuring one periodically on Seattle Astronomy.

Today’s Astro Biz is Orion apartments in Tacoma. We stumbled across Orion during a quickie stay-cation in Tacoma’s Stadium District. It’s in a pretty peachy location near restaurants, pubs, bookstores, and shopping in the district. They’re just a hop and a skip from Wright Park. It looks like they have great views, too.

It’s interesting how many apartment and condo buildings are Astro Bizzes. So far we’ve found Astro, Jupiter, Luna Court, Nova, and Vega. There may be more in the queue. Stay tuned!

More info:

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Mars is here!

It’s been a big year for Mars. The InSight lander is on the way to the Red Planet, scheduled to land November 26 on a mission to take the vital signs of Mars. There’s a big dust storm on Mars just as it reaches opposition this week, its closest approach to Earth since 2003. Oh, and organics have been found on Mars.

We may have buried the lede on that one.

Mars

July 18 image of Mars by the Hubble Space Telescope. (Image credit NASA, ESA, and STScI)

Dave Cuomo and Keith Krumm from the Pacific Science Center were guest speakers at the July meeting of the Seattle Astronomical Society, and discussed all things Mars.

The discovery of organics on Mars is also evidence that science is not necessarily fast. The work came out of a hole the Curiosity rover drilled in a Mars rock way back in 2015. The papers outlining the discovery just came out earlier this year.

“What it found in a rock that is about three-and-a-half billion years old was organic molecules,” Cuomo said. The substance found was kerogen, which Cuomo called, “a gooey precursor to petroleum.”

Cuomo repeatedly stressed that this does not, not, not mean that there is or ever was life on Mars.

“What we have found is evidence that the building blocks for life on Mars certainly did exist three-and-a-half billion years ago,” he said. “This was the first time that we found clear evidence that this was there.”

Cuomo noted that we know a good bit about the history of the surface of Mars.

“Mars certainly was a warmer and a wetter environment that could have supported life, that life could have evolved on,” he said. “What we don’t know—and this is what InSight is going to help us find out—is how long Mars was more Earth-like.” The longer that warm, wet environment lasted, the greater the potential that life could have arisen.

InSight

Krumm noted that InSight is something of an interplanetary RN.

“It’s going to be taking Mars’ vital signs,” he said. It will use a seismometer to take Mars’s pulse, a heat flow probe to measure its temperature, and the Rotation and Interior Structure Experiment, RISE, will check its reflexes, precisely tracking the location of the lander to determine just how much Mars’ north pole wobbles as it orbits the Sun. Cuomo said a big part of the mission’s purpose is to find out if Mars has a molten core today.

“It has volcanoes, so we know at some point in the past it had a molten interior,” he said. “It had a magnetosphere—the remnants of it are frozen in the rocks—but it does not have an active magnetosphere.”

InSight will help us figure out of the core solidified, or if there’s some other reason for the loss of the magnetosphere. Krumm and Cuomo showed this video about the InSight mission.

The Pacific Science Center plans an event for watching the InSight landing on November 26. Watch this space for details!

Dust storm

The rover Opportunity is powered by solar panels, and the dust storm on Mars has blocked the Sun to an extent that Opportunity has shut down. NASA hasn’t heard from Opportunity since June 10. It’s programmed to switch back on every so often, and shut right back down if it doesn’t find power. Cuomo said that can only go on for so long.

“It’s possible it won’t wake up,” he said. If that happened, it would be a sad end to a tremendous run. Opportunity and its twin, Spirit, landed on Mars in 2004 on missions expected to last 90 days. The last contact with Spirit, stuck in the sand, was in March 2010, while Opportunity, up until last month, at least, has been running for more than 14 years.

Opposition

Mars reached opposition to Earth on the evening of July 26 in Pacific Daylight Time, and will be at its closest approach to Earth for the year on Tuesday, July 31. Those dates are different because of the geometry of the elliptical orbits of the two planets. In any case, we’re closer to Mars than at any time since the great apparition of 2003, which is good news for amateur astronomers. The bad news is that the dust storm could foil our attempts to image and observe surface features of Mars. There was word this week, however, that the storm is fading. Bright red Mars will be a good observing target for the rest of the summer and into early fall.

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A cosmic perspective with Jill Tarter of SETI

Jill Tarter thinks that Craig Venter and Daniel Cohen may not have been bold enough when they declared in 2004 that the 21st Century would be the century of biology.

Jill Tarter

The SETI Institute’s Jill Tarter spoke recently at the Rose City Astronomers in Portland, Oregon. (Photo: Greg Scheiderer)

“I think the 21st Century is going to be the century of biology on Earth—and beyond,” Tarter declared during a talk at last month’s meeting of the Rose City Astronomers in Portland, Oregon. Tarter, the Bernard M. Oliver Chair for SETI at the SETI Institute and former director of the Center for SETI Research, thinks there are many ways we might find extraterrestrial intelligence. We might discover it through biomarkers or even artifacts in our own solar system. We could assay the atmospheres of exoplanets looking for biosignatures. We could spot alien “work product” such as structures or signs of engineering. We might even export it, traveling to the Moon, Mars, or even other star systems.

“I think life beyond Earth is a good bet in this 21st Century,” Tarter said, “and when you begin to think about that kind of thing, you really have to reorient your point of view, your perspective. You have to start talking about here and now in a different way, a much bigger point of view, a cosmic perspective.”

Tarter feels that our perspective has changed much since the advent of the space age. Photographs like the Apollo 8 Earthrise or “selfies” by Voyager and Cassini have helped make that happen. We’ve also looked far into the past in viewing distant galaxies.

In the time we’ve been involved in SETI, Tarter says there have been two gamechangers: extremeophiles and exoplanets.

Earthrise

Photos from Space, such as Earthrise by astronaut Willam Anders from Apollo 8, have changed our global perspective. (Photo: NASA)

“Extremeophiles are life as we did not know it until a just few decades ago,” she said, “thriving in places that we once thought completely hostile to life, and they are now illuminating the amazing possibilities for life on our own planet by suggesting more potentially habitable real estate within our solar system and out into the cosmos.”

Similarly, this discovery of thousands of exoplanets has given us more places to look for life.

“Today we know that there are more planets than stars in the Milky Way, and that’s a fundamental change in our perspective,” Tarter said. “When I was a student we knew of nine planets—then lost one!—and didn’t know whether planets would be plentiful around other stars.”

“There is more potentially habitable real estate out there than we ever imagined,” she added, stressing the potential. “We have no idea whether any of it is, in fact, inhabited, but that’s what this century is going to tell us.”

Tarter noted that a big assumption of SETI is that since our technology is visible from a distance, that alien technology might be as well. So we’re looking for something engineered, not a natural occurrence of astrophysics.

“Whether or not SETI succeeds with its optical, infrared, radio searches for signals is going to depend on the longevity of technologies,” Tarter explained, “because unless technologies, on average, last for a long time, there are never going to be two technologies close enough in space to detect one another and coeval in time—lined up at the same time in this ten billion year history of the Milky Way galaxy.”

Tarter said that, in 50 years of SETI, we’ve searched an amount of the cosmos that compares to a 12-ounce glass of water out of the total of Earth’s oceans, so it’s not so surprising that we haven’t yet caught a fish. She adds we’ve been limited by our technology.

“We are beginning to build tools that are commensurate with the vast size of this search, and we understand that the ocean is vast and we are still very, very motivated to go and find what might be out there,” Tarter said. The Allen Telescope Array is a big part of that; you can follow the search at setiquest. There are dozens of other instruments that may provide data to help with SETI, and more than a half-dozen on the drawing boards for the next decade or so.

“This is a hard job,” Tarter said. “This is a lot of very difficult technology to get this job done.”

“Whether or not SETI succeeds in the near term, it has another job to do,” Tarter concluded. “Whether or not it ever finds a signal, it has another job to do. And that is holding up a mirror to all of us on this planet and showing us that in that mirror, when compared to something else out there, we are all the same. Talking about SETI, thinking about SETI, listening to talks about SETI, helps to transfer and to encourage this cosmic perspective. It helps to trivialize the differences among us.”

Tarter encouraged everyone to go home and set their discriptions on their social media profiles to “Earthling,” and to start thinking and acting from that perspective.

“SETI is a very good exercise at working globally to solve a problem,” she said, “and there are many problems that we are going to have to solve quickly in the near term, and do so as a global community.”

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Celebrating three years of Astronomy on Tap Seattle

Astronomy on Tap Seattle observed its third anniversary last month, and celebrated by breaking format, with updates on talks from the past year and some new tidbits of information.

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.

Selfie from space

Selfie from space: Earth as observed by Kepler in December. (Image: NASA)

“We guilted them into taking this picture that we wanted for no other value than just to have this amazing image,” Davenport said. He noted that NASA has a long tradition of taking photos of the home planet, starting with the “Earthrise” photo from Apollo 8 and going through the “Pale Blue Dot” image from Voyager and the more recent pic of Earth from Cassini at Saturn.

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 senstive 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.

Trappist-1 system“These are planets that could be a lot like Earth, that could potentially support life,” said Dr. Rodrigo Luger, adding that this is an active area of research. Luger said it’s interesting that all seven planets are in orbital resonance.

“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 looking for 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.

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The search for Earth 2.0

Astronomers have to date discovered more than 3,700 exoplanets—planets in orbit around stars other than our Sun. With each discovery, someone wants to know if the newly discovered planet is like Earth.

Elizabeth Tasker

Elizabeth Tasker at Astronomy on Tap Seattle.

Elizabeth Tasker thinks that’s not a very good question. Tasker, associate professor at the Japan Aerospace Exploration Agency, Institute of Space and Aeronautical Science and author of The Planet Factory: Exoplanets and the Search for a Second Earth (Bloomsbury Sigma, 2017) gave a talk at the most recent edition of Astronomy on Tap Seattle. She said that some of the exoplanets confirmed so far have at least a little resemblance to Earth.

“Roughly one third of those are approximately Earth-sized, by which I mean their physical radius is less than twice ours,” Tasker said. News media often wish to leap from that to describing a planet as Earth-LIKE, but Tasker said we don’t have nearly enough information to make that sort of call. Our current methods of detecting an exoplanet can give us either its radius or its minimum mass, and a pretty good read of its distance from its host star.

“The problem is neither of those directly relates to what’s going on on the surface,” Tasker noted. Part of the challenge is what Tasker feels is the somewhat oversimplified notion of the “habitable zone” around a star, a band of distance in which liquid water—a key to life as we know it—could exist on a planet’s surface.

“Like all real-estate contracts, there is small print,” Tasker said. “Just because you’re inside the habitable zone doesn’t mean you’re an Earth-like planet. Indeed, of all the planets we’ve found in the habitable zone around their stars, there are five times as many planets that are very likely to be gas giants like Jupiter than have any kind of solid surface.”

Another misleading metric that has been used is something called the “Earth similarity index.” This method compared exoplanets to Earth on the basis of properties such as density, radius, escape velocity, and surface temperature.

“None of these four conditions actually measure surface conditions at all,” Tasker said, pointing out that the index didn’t take into account such features as plate tectonics, a planet’s seasons, it’s magnetic fields, greenhouse gases, or existence of water. We can’t observe any of those things about exoplanets yet. As an example of the flaws of the index, Venus came out at 0.9, pretty similar to Earth, which is at 1.0 on the zero-to-one scale. While Venus is about the size of Earth and is around the inner edge of the Sun’s habitable zone, its surface temperature could melt lead. Not very Earth-like, or habitable. It’s one of the reasons that the index is seldom used these days. So we don’t have much of a clue about conditions on any of the known exoplanets.

“Our next generation of telescopes is going to change that,” Tasker said. She noted that NASA’s James Webb Space Telescope is scheduled to launch next year, the ESA’s Ariel in 2026, and the UK’s Twinkle in the next year or so.

“All of these are aiming at looking at atmospheres, and these may be able to tell us what is going on on the surface, and may even give us the first sniff of life on another planet,” Tasker said. “Maybe then we’ll be able to talk seriously about Earth 2.0.”

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