Tag Archives: Astronomy on Tap Seattle

Astronomy behind the scenes: great successes and colossal blunders

The most recent gathering of Astronomy on Tap Seattle promised to take us inside the way science is really done, and delivered with tales of unexpected successes and a colossal fail that left a team of cosmologists with cosmic egg on their faces.

Leah Fulmer

Leah Fulmer, a second year graduate student in astronomy at the University of Washington, gave a talk titled “Falling with Style: How Astronomy’s Most Intriguing Discoveries Happen by Accident.” Fulmer noted that astronomers have lots of choices when it comes to their research. They can select which part of the sky to examine, what to look at, how long to look, how often to look, and in which wavelengths of light to look, just to name a few. There’s lots of potential there.

“Every time we look at the universe in a new way we discover new phenomena that we never even expected to see,” she said. Fulmer shared three historical examples of such scientific serendipity.

The first was the detection of the cosmic microwave background (CMB) back in the 1960s. At the time it was theorized that 400,000 years after the Big Bang the CMB would have left its energy throughout the universe as a result of the event. Arno Penzias and Robert Wilson had access to a big radio telescope and were working on doing some radio astronomy. The problem was that they couldn’t tweak out some pervasive and persistent noise from their observations. Meanwhile down the road some theorists at Princeton were trying to figure out how to detect evidence of the CMB. Penzias and Wilson had already done it!

“By accident they took this telescope that NASA had built for satellite communicaiton, they stuck it out there, and they found literally the origins of the universe,” Fulmer said. “This changed our understanding of astronomy and physics as we know it and it was a really, really big deal, just by looking at something in a new wavelength.”

More recently the operators of the Hubble Space Telescope decided to pick out an empty, black part of the sky and have the scope stare at it for 100 hours. Many scientists thought this was a bit daft.

The Hubble Deep Field. Image credit: Robert Williams and the Hubble Deep Field Team (STScI) and NASA/ESA

“They found what’s now known as the Hubble Deep Field,” Fulmer said. “They found an incredible plethora of galaxies that they never expected to see.” It revolutionized our understanding of the number of galaxies in the universe and added greatly to the types, shapes, and sizes of galaxies that we know about.

The Kepler Space Telescope found thousands of exoplanets, and collected data on so many things that scientists couldn’t possibly look at all of them. They enlisted citizen scientists through Zooniverse to help examine objects. Participants looked at the data and among their findings is an oddly behaving star for which its light curves defy explanation. We now know of it as “Tabby’s Star,” after astronomer Tabetha Boyajian, who wrote the paper about the discovery.

“To this day we don’t actually know what this star is,” Fulmer said. There have been lots of ideas about the odd light curves, from a random pack of asteroids that might be irregularly blocking light, some sort of cosmic catastrophe that kicked up debris, and even giant space structures built by an unknown civilization.

“It’s very precarious for an astronomer to suggest that this might be aliens,” Fulmer laughed, noting that the media would have a field day with that sort of thing.

The potential for discovering strange new things in the universe is about to increase. The Large Synoptic Survey Telescope is scheduled to go online in a few years, and when it does it will collect petabytes of data, doing a complete sweep of the sky every few nights for a decade.

Fulmer said a big part of her job in the project will be to help “develop an algorithm that is going to be able to systematically identify the things that we’ve never seen before.” That’s a tall order, combing all of that data for things we know about, things that have been theorized, and those that come out of the blue.

“We don’t what surprises we might find,” Fulmer said, “but that’s what makes it so exciting.”

Oops

Samantha Gilbert, a first-year graduate student in astronomy at the UW, told a story about a colossal and embarrassing failure. Her talk was titled, “Leaving the Competition in the Dust: A CMB Case Study.”

“The story I want to tell you tonight has everything: It has science. It has drama. It has egos. It has really esoteric vector math,” Gilbert said to laughter. “It encapsulates some of the things that are really wrong with how some people do science today.”

The story also involves the cosmic microwave background. Cosmologists are trying to figure out what happened between the Big Bang and the formation of the CMB 400,000 years later. A leading theory is that there was a period of inflation in the moments after the Big Bang during which the universe expanded rapidly. If that happened, it would have created gravitational waves, and those waves would have left behind a pattern in the CMB that we could recognize, called “B-mode polarization.”

A map of the cosmic microwave background. Image credit: NASA / WMAP Science Team

“B-mode polarization is an extraordinarily difficult thing to detect,” Gilbert said, “but proving it exists, proving that inflation really happened by detecting the traces of inflationary gravitational waves” would be Nobel Prize-worthy.

That’s where the intrigue starts. One group striving for this discovery had an experiment called BICEP (Background Imaging of Cosmic Extragalactic Polarization), which was followed by BICEP2, which had more sensitive detectors than the first version and more of them. They found what they were looking for. In fact, the signal of B-mode polarization was even stronger than anticipated. The team declared the discovery during a 2014 news conference at Harvard, issued a video, broke out the bubbly, and in general whipped up lots of hoopla about the discovery.

In the following months some 250 papers were published in response to BICEP2. One of them was from BICEP’s main competitor, the Planck Experiment, and their point was that BICEP’s discovery was bunk and that what they detected was not B-mode polarization, but cosmic dust.

“The fact that BICEP2 had so confidently announced a result that was so quickly disproven had a rippling effect throughout the community,” Gilbert said. “Scientists were horrified because they thought, ‘now the public is going to discredit us, they’re not going to trust us.’ Journalists were also horrified because they felt they had a role in spreading disinformation.”

They were also seeing an ugly side of the scientific community.

The need for speed

How did this happen? BICEP principal investigator Brian Keating wrote a book about their process, titled Losing the Nobel Prize (W.W. Norton & Company, 2018). Gilbert summarized their decision-making.

She said BICEP2 only looked at one wavelength of light so they could get the results as quickly as possible. They knew about the possibility of cosmic dust, but didn’t have the tools to distinguish between dust and B-mode polarization. The Planck folks were thought to have the data, and BICEP asked them to share. They declined.

This led BICEP to jump to the conclusion that Planck also had evidence of B-mode polarization and were aiming to scoop them on the discovery and dash their dreams of a Nobel Prize. So they hurried to make the announcement. This might have worked out OK, if they’d been right, but the BICEP group made one other glaring error.

“They actually hadn’t put their paper through peer review,” Gilbert noted, generating groans among the science-savvy audience at Astronomy on Tap.

“That is a no-no,” she understated. “That is a bad thing to do because peer review is what makes science credible in the first place. It’s a really important check against the dissemination of junk science. You really need other scientists to independently assess your results.”

Gilbert said the bad decisions were all motivated by fear.

“Overly competitive environments are part and parcel of an individualistic conception of science and an individualistic conception of science says that the most important thing is to get a result before your competition,” she said. “When that’s the environment that you’re working in you tend to make decisions based on fear.”

“I would argue that the reason that BICEP2 made these decisions based on fear is that they were operating in such a toxically competitive environment that it became dysfunctional,” Gilbert said. “Whether you think competition is really good for science, really bad, or somewhere in between, I think that this case study shows us that it’s really worth thinking about the ways that we systemically and interpersonally encourage competition, and how that might jeopardize our ways of knowing.”

Gilbert said there’s hope for the future. The hunt for B-mode polarization continues, and BICEP and Planck are teaming up going forward, combining their resources and know-how in the work.

“Competition might be the most efficient way to A result, but collaboration is probably the most efficient way to a RELIABLE result,” she said.

Astronomy on Tap Seattle is organized by graduate students in astronomy at the University of Washington.

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Celestial Pig Pens and new tricks for old scopes

It takes a lot of detective work to figure out the nature of a type Ia supernova. Celestial Pig Pens and new tricks from old telescopes are contributing to the effort. That’s what we learned at the most recent meeting of Astronomy on Tap Seattle.

Messy Siblings: Supernovae in Binary Systems

Dr. Melissa Graham is a project science analyst for the Large Synoptic Survey Telescope, working out of the Astronomy Department at the University of Washington. Her main research focus is supernovae. In particular, she’s doing a lot of work on type Ia supernovae, which occur in binary star systems. One of the stars involved will be a carbon-oxygen white dwarf star.

“It’s a star that wasn’t massive enough to fuse anything else inside the carbon layers,” Graham explained. Outer layers of hydrogen and helium are thrown off in a planetary nebula phase, so the carbon and oxygen are what’s left.

Melissa Graham
Melissa Graham. UW photo.

“Carbon-oxygen white dwarf stars are very compact, very dense, about the size of the Earth but they can be up to about 1.4 times the mass of the Sun,” Graham said. These stars are pretty stable as stars go, so they don’t blow up under normal circumstances.

“When we do see these kind of supernovae that are clearly the explosion of carbon-oxygen white dwarf stars we have to wonder why,” she said. It turns out there are two possible scenarios. The binary can be a pair of carbon-oxygen white dwarf stars that spiral in on each other, merge, and then explode. Or the binary can include one white dwarf and a more typical hydrogen-rich companion star.

“In this case the companion star can feed material onto this carbon-oxygen white dwarf star, might make it go over 1.4 solar masses, become unstable, and then explode,” Graham said.

Which is which?

The key to figuring out which of these scenarios actually occurred is to take a look at the area around the supernova. If the companion is a more hydrogen-rich companion star, the neighborhood can get a little messy.

“It’s sort of like a celestial Pig Pen star that leaves a lot of material lying around,” Graham said. A blast from a supernova can interact with this material and cause it to brighten. The trouble is that astronomers typically only observe type Ia supernovae for a couple of months; they fade quickly. So if this extra material is far away from the event, they might not see the interaction. The answer is patience, to look at the supernova sites for up to 2-3 years after.

Graham did exactly that, using the Hubble Space Telescope to keep an eye on the locations of 65 type Ia supernovae.

“Out of these 65, I very luckily found one” in which there was brightening much later. They checked the spectrum of the light and found hydrogen, a sure sign that the companion in this particular type Ia supernova was a Pig Pen. Graham suspects that up to five percent of such explosions involve messy sibling stars.

Graham looks forward to having the Large Synoptic Survey Telescope (LSST) come on line. She expects it will find some 10 million supernovae in a decade.

“This marks a massive increase in our ability to both find and characterize supernovae,” she said.

Old scope, new tricks

While we wait for LSST an old workhorse telescope is doing interesting work in a similar vein. Professor Eric Bellm of the UW works with the Zwicky Transient Facility (ZTF), which uses the 48-inch telescope at Palomar observatory in California. The scope is a Schmidt, completed in 1948, and for years it was the largest Schmidt telescope in the world. It’s main function at first was to use its wide-field view of the sky to create maps that helped astronomers point Palomar Mountain’s 200-inch Hale Telescope.

Eric Bellm
Eric Bellm. UW photo.

The 48-inch was used to do numerous sky surveys over the years. It discovered many asteroids, and Mike Brown used it to find the dwarf planets he used to kill Pluto. The old photographic plates gave way to modern CCDs, and Bellm became the project scientist for the Zwicky Transient Facility—named for astronomer Fritz Zwicky, a prolific discoverer of supernovae—in 2011.

They outfitted the scope with a new camera with 16 CCDs that are four inches per side. They got some big filters for it and put in a robotic arm that could change the filters without getting in the way of the camera. They started surveying in March of last year and can photograph much of the sky on any given night.

“That’s letting us look for things that are rare, things that are changing quickly, things that are unusual,” Bellm said.

Examples of what the ZTF has found include a pair of white dwarfs that are spinning rapidly around each other, with a period of just seven minutes. They can see the orbits decay because of gravitational wave radiation. It has discovered more than 100 young type 1a supernovae. And it found an asteroid with the shortest “year” of any yet discovered; its orbit is entirely within that of Venus.

It’s doing the same sort of work that the LSST will do when it comes online.

“It’s super cool that we’ve got this more than 70 year old telescope that we’re doing cutting-edge science with thanks to the advances of technology,” Bellm said.

Astronomy on Tap Seattle is organized by graduate students in astronomy at the University of Washington, and typically meets on the fourth Wednesday of each month at Peddler Brewing Company in Ballard. The next event is set for September 25.

A surprise discovery from Apollo 11 lunar samples

As we look back at the 50th anniversary of the Apollo 11 Moon landing, Toby Smith notes that the most interesting science that came out of the mission was a bit of a surprise. Smith, a senior lecturer in astronomy at the University of Washington, gave a talk at the most recent meeting of Astronomy on Tap Seattle.

“There’s only one reason Apollo existed—to beat the Soviet Union to the surface of the Moon,” Smith noted. Few considered the mission to be scientific. “It wasn’t fully embraced by the scientific community even in its day, even among planetary scientists.”

But they figured as long as they were there, they should do some sort of science.

“This little bit of science they did fundamentally changed how we view not only the Moon, but the Earth-Moon system and our solar system,” Smith said.

The Apollo 11 landing site, the Sea of Tranquility on the Moon, is essentially an ancient lava flow, a featureless plain of cooled volcanic rock, Smith said. Think of it like Big Island of Hawaii, except you don’t really see the solidified lava on the Moon. The surface is soft, ground down and rounded off into a soft powder by billions of years of impacts. As Neil Armstrong observed just after his first step, it has the consistency of flour. That consistency almost accidentally led to the mission’s best science.

Moon rock box
An Apollo Lunar Sample Return container on display at the Destination: Moon exhibit at the St. Louis Science Center in 2018. (Photo: Greg Scheiderer)

Armstrong spent about 15 minutes of the two-and-a-half hour Moon walk picking up rocks and putting them into a box. At the end he collected nine scoops of lunar regolith and dumped it into the Apollo Lunar Sample Return Container (a fancy NASA term for the case for rocks) as sort of a packing material so the larger rocks wouldn’t clatter around. If they’d taken any styrofoam peanuts he might have used those instead.

Naturally, when this material was brought back to Earth, the scientists looked at it, and Smith said it just might be the most studied geological sample ever.

Smith noted that the regolith is highly angular; lunar dust is sharp.

“This is not material that was broken up by being tumbled,” he said. “This is material that was broken up by being fractured by impacts.”

It’s a diverse sample. It contains basalt, breccia (material created by impacts that shatters and sometimes melts back together), and impact spheres. There was also one unusual, bright white material in the collection. It turned out to be anorthosite, which makes up about four percent of the sample.

“It represents a piece of the original crust of the Moon long since destroyed by four and a half billion years of impacts,” Smith explained. Anorthosite is an igneous rock, like basalt, that comes from the cooling of melted rock. Basalt is created when lava moves across the ground, but Smith noted that anorthosite doesn’t work that way.

“Anorthosite forms in big pools of lava, huge pools of lava, huge chambers of lava,” he said. “As these chambers of lava slowly cool over time, the anorthosite floats to the top.”

“If this was found on the Moon it must mean that at some point early in the Moon’s history it must have been almost completely molten,” Smith added. This information made scientists re-think their notions about the origins of the Moon.

“Before Apollo there was no indication that the whole, entire Moon was almost completely melted,” he said.

The leading theory about the formation of the Moon these days is that something pretty big, about the size of Mars, smacked into the early Earth, and that material flung into space by the impact eventually coalesced into the Moon. The catch is that computer simulations of this event don’t often result in a completely molten Moon. So more study is needed. The lunar samples have been under constant scrutiny for the last 50 years, and Smith says he’s interested to see what new information can be gleaned from those samples as new analytical technology is developed.

Astronomy on Tap Seattle is organized by graduate students in astronomy at the University of Washington. The next gathering is set for Wednesday, August 28, 2019 at Peddler Brewing Company in Ballard.

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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.

LSST to the rescue

We hope the Large Synoptic Survey Telescope (LSST), under construction in Chile on a timeline that would have it begin science work in 2022, works. There are a bunch of astronomers banking on it to make their lives a lot easier. A group of them—the LSST Solar System Science Collaboration—met earlier this month in Seattle, and four of them gave talks at a special edition of Astronomy on Tap Seattle at Peddler Brewing Company in Ballard.

David Trilling of Northern Arizona University noted that the LSST will have an 8.4-meter mirror and a camera the size of a small car.

“In terms of telescopes, this is a really, really, really big machine,” he understated. That car-sized camera will boast 3.2 billion pixels.

“You’d need 1,500 HDTV screens to look at a single LSST image,” Trilling said. LSST will scan the entire night sky every three to four nights for ten years.

“That’s about ten terabytes of data every night, which is a huge computational challenge,” he noted.

It’s an asteroid. It’s a comet. It’s complicated…

Michael Mommert of Lowell Observatory studies asteroids and comets. He said that sometimes it’s difficult to tell one from another. An asteroid can look like a comet if the asteroid is “active.” This could be because it collided with something else, or it is spinning rapidly, or it was warmed by its proximity to the Sun.

“If we can understand those active asteroids we can better understand the average asteroid,” Mommert said. “We can learn a lot about the mechanisms that are going on in asteroids from those active asteroids.”

Similarly comets can go dormant, with no tail, and look more like asteroids. As they often share similar properties, Mommert said comets and asteroids are on something of a continuum rather than being two distinct types of objects.

In his research Mommert is tracking about 20 active asteroids and 50 dormant comets. He figures he spends 30 nights per year using a telescope. He’ll be able to cut down that time tremendously with LSST; he’ll be able to find his targets and pull data collected by the telescope.

“LSST will improve our understanding of small body populations,” Mommert said. “Asteroids, comets, active asteroids, everything that is out there.”

Tales from the Outer Solar System

Kat Volk of the University of Arizona focuses her research on objects in the outer solar system. Pluto, Eris, and other far-out objects have been discovered by comparing photos of an area of sky and looking for something that moved. In fact, Pluto was the first object discovered in this way.

There are about 2,000 known objects in the Kuiper Belt. That’s about how many asteroids we knew of a century ago.

“Kuiper Belt science is a hundred years behind Asteroid Belt science because these things are just so much more difficult to find,” Volk said, because they’re far away, faint, and move slowly. “We had to wait until we had digital cameras and computers to process those images.”

Volk said we probably have discovered all of the 10-kilometer asteroids and most of the 1-kilometer ones. They’re easier to spot because they’re brighter, and there’s money for the hunt because of the potential threat asteroids pose to Earth.

“For comparison, the smallest ever observed Kuiper Belt object is 30 kilometers across, very roughly,” Volk said, adding that we only found that one because the Hubble Space Telescope was used to look for another target for the New Horizons mission after it passed Pluto.

“We’re pretty incomplete in terms of our object inventory in the outer solar system,” Volk said. She said LSST will change that.

“They expect 40,000 new Kuiper Belt ojects,” Volk said. “It’s going to be an entirely new era for the Kuiper Belt with a huge playground of new objects to look at.”

“I am realy excited to see what we’re going to find with LSST, and it’s going to completely revamp our idea of the outer solar system.”

A Crash Course in Asteroid Defense

Andy Rivkin of the Johns Hopkins University Applied Physics Laboratory said that even a 20-meter asteroid packs a wallop when it smashes into Earth. That was roughly the size of the Chelyabinsk meteor in 2013.

Doing the math tells us that there should be about 10 million objects of that size zipping around the solar system, but so far we’ve found only around 10 thousand of them. Back in 2005 Congress told NASA to find 90 percent of objects 140 meters or larger.

“LSST is going to be a critical piece in reaching this goal,” Rivkin said, “and we expect that by 2034 about 86 percent of hazardous asteroids will be found.”

So, what do we do when we spot one headed our way? Rivkin said that for really small ones, like Chelyabinsk, and really large ones, the best idea might be duck and cover. There’s not much to be done about something very large, and small ones don’t pose much of a threat. For those in between, a few options are viable. For one, we could try to deflect the asteroid with a nuclear bomb.

“A lot of people are uncomfortable with nuclear explosions in space, for good reason, and so there’s been a lot of interest in having something else that could work,” Rivkin said.

That something else is a kinetic impactor, which is a fancy way of saying we’ll just smash something into the asteroid to change its speed, and therefore its orbit. It’s a fine idea in theory, but we have no idea if it would actually work. Rivkin is involved in a project that will give it a try.

It’s called DART, which is for Double Asteroid Redirection Test. DART is on schedule to launch for the asteroid Didymos in June of 2021, and then crash into its satellite, nicknamed “Didymoon,” in October 2022. Astronomers will watch through ground-based telescopes and see what happens. Rivkin called it a dress rehearsal for the day we might have to do something about an incoming asteroid.

“A dress rehearsal for, needless to say, a performance we hope never to actually stage,” he said, “demonstrating that we could do this, allowing us to pin these computer simulations to something real, allowing us to better understand asteroidal properties, and giving us a lot of science as an ancillary benefit.”

Astronomy on Tap Seattle is organized by graduate students in astronomy at the University of Washington.

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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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Astronomy on Tap and a blue moon this week

It’s a light calendar of astronomy events for Easter week, but you can celebrate Astronomy on Tap Seattle’s third birthday and enjoy our second blue moon of the year!

Happy three to AOT

AOT March 28It’s hard to believe it’s been three years since a group of graduate students in astronomy started up the Astronomy on Tap Seattle lecture series, but this week’s edition will mark the 36th consecutive month that they’ve offered interesting talks, astronomy trivia, fun prizes, and great beer. Head to Peddler Brewing Company in Ballard at 7 p.m. Wednesday, March 28 for updates on the astronomy AOT has covered in the last year, and a look at the exciting new science that has come out recently—neutron star mergers, new planets, and more!

It’s free, but buy some beer. Bring your own chair to create premium, front-row seating.

Blue moon

It turns out “once in a blue moon” isn’t all that rare! Saturday’s full moon will already be the second one this year, at least by the definition that a blue moon is the second full moon in a calendar month. We had a blue moon in January, too; see the video below of Seattle Astronomy’s Greg Scheiderer talking on KING-TV’s New Day Northwest about the super blue blood moon.

The next blue moon after this week will be on Halloween in 2020.