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 at Astronom on Tap
Seattle. Photo: Greg Scheiderer.

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.”

Astronomy's neglected stepchild

Robert Reeves has been an astronomer for nearly 60 years. The Moon was his first love; he shot his first photograph of it in 1959, and laments that it isn’t such a popular target for amateur astronomers any more.

Astrophotographer and author Robert Reeves was the guest
speaker at the annual banquet of the Seattle Astronomical
Society on Jan. 28, 2018. Photo: Greg Scheiderer

“The Moon is not just that big ball of light pollution in the sky,” said Reeves during his keynote talk at the Seattle Astronomical Society’s annual banquet last month. “The Moon used to be a target for American technology. The Moon was a place to be explored; it was a destination.”

Reeves was interested in the Moon even before there was a space program. We were all agog during the race to land on the Moon, but when the race was won many moved on to other things.

“Back then American heroes rode a pillar of fire and dared to set foot on another world,” Reeves said. “The scientific mindset, the desire to explore the solar system was there. That was a time when America was only limited by its imagination; we could do anything we wanted to do.”

Alas, Reeves notes, politics is different now.

“America has lots its will, it’s lost the guts to go into deep space,” he said. “We’ve been rooted in low-Earth orbit for four decades.”

“Space exploration is not the same, but the Moon that we wanted to go to still beckons us,” he added.

Bringing the Moon back

Reeves’s talk was titled Earth’s Moon: Astronomy’s Neglected Stepchild. He aims to turn that around.
“I’m here to bring the Moon back,” he said. “The Moon is still a viable target; we can see it from our own back yard.”

Reeves is a prolific writer about astronomy. His first published article appeared in Astronomy magazine in 1984. Since then he’s written some 250 magazine articles and 175 newspaper columns about the topic. In fact, just days after his talk here the March 2018 issue of Astronomy arrived, including an article and photos by Reeves about hunting for exoplanets. His mug also appears, along with one of his lunar photographs, on a back-cover advertisement for Celestron.

Reeves has written five books in all, including three how-to manuals about astrophotography: Wide-Field Astrophotography: Exposing the Universe Starting With a Common Camera (1999), Introduction to Webcam Astrophotography: Imaging the Universe With the Amazing, Affordable Webcam (2006), and Introduction To Digital Astrophotography: Imaging The Universe With A Digital Camera (2012). All are from Willmann-Bell.

Reeves feels the webcam book helped launch a whole industry and trained a generation of astrophotographers. He points out that back in the 1960s you could count the number of good astrophotographers with the fingers of one hand. Now there are thousands of people turning out great images, and they all get to use superior gear.

“Amateur instruments off the shelf today just blow away what the pros used to do on the Moon, and it’s relatively easy to do this,” Reeves said. I asked Reeves if he laments the passing of film photography. He said he did, a little, noting with a laugh that he has four decades worth of photography that is obsolete! But he said the fact that he can turn out more better-quality images in less time with digital makes up for that.

Check out Reeves’s website for a image-processing tutorial, to buy prints and posters, and find lots of other lunar photography information.

Asteroid 26591 is named Robertreeves and asteroid 26592 is named Maryrenfro after his wife; Renfro is her maiden name. It is believed they are the only husband and wife with sequentially numbered asteroids named after them! Robert noted that his takes about four years to orbit the Sun, while Mary’s goes around in about 4.4 years.

“Every ten years I catch up to her,” he said, “so for eternity I’m going to be chasing Mary around the solar system.”

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Books by Robert Reeves:

Beyond Pluto with New Horizons

Ron Hobbs has been a NASA JPL Solar System Ambassador almost since that program started just over 20 years ago. What began as an effort to recruit volunteers to help keep people informed about the Galileo mission to Jupiter soon expanded to include most other JPL missions.

“Education and public outreach is very important to NASA,” Hobbs explained. “They’re spending Americans’ money to go out and explore the universe, and they want to make sure that they get the information out to everyone who’s interested in it.”

New Horizons

There’s a lot of interest. Hobbs and I talked recently about New Horizons, which did a historic fly-by of Pluto in 2016 and is now napping while whizzing through space for a New Year’s date with the romantically named 2014 MU69. This object, discovered in 2014 using the Hubble Space Telescope specifically to find a potential place for New Horizons to visit after Pluto, is in a relatively undisturbed part of the Kuiper Belt. Observations made of MU69 suggest that it is either oblong or a binary object, perhaps a contact binary. Recent research has suggested that most early planetesimals were binaries.

“It is very likely that it is one of these primordial planetesimals,” Hobbs said. “So in some senses the exploration of MU69 may be more important than the exploration of Pluto. And that’s saying a lot.”
Hobbs shared a couple of favorite bits of information about New Horizons. For one, the spacecraft is carrying human remains.

“Clyde Tombaugh, the discoverer of Pluto, will become the first human being to have their remains interred in interstellar space,” Hobbs noted.

New Horizons Principal Investigator Alan Stern presents a
plaque to Venetia Burney Phair in December 2006,
commemorating the name “Venetia” for the New Horizons Student
Dust Counter. Phair passed away in 2009. Photo: NASA

One of the instruments aboard New Horizons is the The Venetia Burney Student Dust Counter, named after the English schoolgirl who suggested the name for Pluto way back in 1930. The instrument was built and managed by students at the University of Colorado.

“It is the first student built instrument on a major NASA probe, ever,” Hobbs said. It’s just one example about how the mission is becoming a world-wide effort. Hobbs marvels that we are all space explorers.

Scientists are searching for another possible target for New Horizons after it does its flyby of MU69. Hobbs said the craft has limited fuel, so it’s unclear how much more it can maneuver.

Listen to the podcast to learn more about New Horizons and how ordinary citizens are participating in science.

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Hobbs also recommends a recent NASA “Gravity Assist” podcast featuring New Horizons principal investigator Alan Stern.

Exploring alien moons

The search for extraterrestrial life keeps getting smaller in scale. It’s difficult to discover planets around other stars, but now scientists are looking for exomoons and alien bacteria. Two University of Washington graduate students shared their work at an Astronomy on Tap Seattle gathering at Peddler Brewing Company in Ballard last week.

To date more than 3,500 exoplanets have been discovered in orbit around stars other than our Sun, but we haven’t seen an exomoon orbiting any of those planets. Tyler Gordon, a second year grad student in astronomy and astrobiology at UW, thinks it’s only a matter of time before we do.

“We have every reason to expect that there are a lot of moons out there in the universe, probably many more than there are exoplanets,” Gordon said. Thinking about our own solar system, he pointed out that there are 19 moons that are big enough to be rounded by their own gravity, which is more than twice as many such moons as there are planets.

Despite the fact that no exomoons have yet been found, Gordon said there are three good reasons to look for them:

• They might be habitable
• The presence or absence of a moon can give a clue about how a planet formed
• A moon can be a factor in a planet’s habitability

There are two reasons for that third point. Moons can raise tides, and some scientists think that tides battering the shore on early Earth delivered nutrients and created places for life to develop. In addition, moons can influence a planet’s orbital characteristics, especially obliquity, and help stabilize oscillations of its rotational axis.

“An exomoon can keep a planet from tumbling back and forth onto its side and can insulate it from having really extreme changes in seasons, which is something that we think could be very bad for life,” Gordon said.

Where are they?

It’s been hard enough to identify exoplanets, and there’s an obvious challenge in hunting for exomoons.

“Exomoons are probably really small, and small is a problem because small things are really hard to see,” Gordon noted.

Just how small are moons? Gordon explained that observation and modeling have found that the mass of a planet’s satellites generally scales with the mass of the planet itself. For any given planet, “We expect that the total mass of its satellites adds up to between one ten-thousandth and two ten-thousandths of the mass of their host,” Gordon said.

Thus to find an exomoon as big as Earth—something we could actually see—its host planet would have to be about 30 times the mass of Jupiter. Something that big probably wouldn’t be a planet; it would more likely be a brown dwarf.

Finding an exomoon

Most of the exoplanets discovered to date have been spotted because they cause a dip in the light we see coming from their star when they transit in front of it. An exomoon would do the same thing, but Gordon said there are a couple of challenges. Since the exomoon would be far smaller than the planet, so would the dip it would cause. Plus, sometimes the exomoon will be ahead of, behind, or blocked by the planet, making patterns more difficult to tease out of the data.

Gordon noted that a team from Columbia University recently tried to do that by looking at a ton of Kepler data and searching for scattering called the “orbital sampling effect.” In all of the data they found exactly one potential signal for an exomoon; it’s in orbit around the planet Kepler-1625b. This is a big planet, about ten times the mass of Jupiter, and the moon—Kepler-1625bi—is about the size of Neptune, which is way bigger than would be expected according to the scaling rule. Gordon said that raised a lot of questions.

“Is Kepler-1625b even a planet if it’s that’s big? Is the moon actually even there at all?” he asked. “And if it is there, how can such a large moon form?”

The Columbia team used the Hubble Space Telescope to look at the system back in October, but analysis of the data and any answers to those questions have yet to be published.

Gordon said that the James Webb Space Telescope will be a big help to exomoon hunters. While Kepler looked in the visual, JWST is equipped for other wavelengths.

“By using JWST’s ability to see in different parts of the electromagnetic spectrum we may be able to disentangle the transit of an exomoon from stellar variability that could obscure that transit,” Gordon said.

Space bacteria

Max Showalter is looking for stuff way smaller than exomoons. He’d like to spot interplanetary bacteria.

Showalter, a Ph.D. student in oceanography at the UW, gave a talk titled, “Looking for Life When the Trail Goes Cold.” He noted that the hunt for biosignatures is at the heart of the search for life. Biosignatures can be chemical, say oxygen in an atmosphere. They can be structures, such as fossils. They could be biological molecues like amino acids or nucleotides.

“They tell us that either life has been there in the past, or life is there now, or life could be there in the future,” Showalter said. “We want lots of biosignatures all telling us the same thing in order for us to decide that there’s life.”

Showalter would add another biosignature to the list: movement. After all, there’s no better sign of life than if something comes up and waves at you. Still, when you’re looking for microbial life, the tough questions are whether bacteria swim in space, and how we’ll see them if they do.

“It’s hard enough to see microbes on Earth, let alone millions of miles away,” Showalter noted. His research specialty is studying things that live in sea ice. When salt water freezes, the salt can either fall out or get stuck inside the ice. If it’s inside, the salt gets concentrated and melts pockets of ice, creating what are called brine pores.

“These brine pores are great because they make a really good habitat for a lot of things to live inside the ice,” Showalter said.

Ice-beings on Earth

Showalter has looked at bacteria from Arctic sea-ice on site with a microscope called SHAMU, which stands for “Submersible Holographic Astrobiology Microscope with Ultra-resolution.” SHAMU works on principles of holography. A laser in a box is split into two beams. One beam goes through the brine sample, the other goes straight to a camera. The waves of light interfere with each other, and computer analysis can create a hologram: “A 3-D image of a tube of liquid where you can see bacteria swimming,” Showalter said. (Read a longer article about SHAMU from a talk Showalter gave at Town Hall Seattle in 2016.)

The application for SHAMU in the search for life is at places like Saturn’s moon Enceladus and Jupiter’s moon Europa, both of which have salt water oceans under thick crusts of ice. Some of this salt water shoots out of geysers on the moons and into space.

“Which presents a really incredible opportunity for us as astrobiologists—or astronomers if you’re one of those people—to be able to sample that ocean without having to drill through eight kilometers of ice!” Showalter said.

An upcoming NASA mission called Europa Clipper will take a shot at that. The spacecraft is presently scheduled for launch some time between 2022 and 2025. SHAMU isn’t going, and none of the instruments selected for the mission will be looking for bacterial motility, but Showalter holds out hope that motility will prove to be a useful biosignature in the future.

He said he doubts that Europa Clipper will find life, but expects it will come across some tantalizing clues.

Tomorrow morning: Super blue blood Moon

A total lunar eclipse is a pretty cool event in its own right. Add in a blue moon and a super moon and you’ve got three celestial treats in one. Tomorrow morning we on the west coast may enjoy the first super blue blood moon visible in North America since 1866—if the weather cooperates.

Seattle Astronomy writer Greg Scheiderer talked about the super
blue blood moon on the KING 5 television program New Day
Northwest January 30. His planets tie was a hit with the studio
audience. Photo: Greg Scheiderer.

A lunar eclipse isn’t all that rare. They can happen two or three times a year, but tomorrow’s will be the first visible (theoretically) from the Seattle area for a couple of years. The blue moon, under the generally accepted modern definition of the second full moon in a calendar month, isn’t quite so rare as the phrase “once in a blue moon” would suggest. On average, a blue moon happens once every 2.7 years. This year is a bit of an oddity, as not only will we have a blue moon tomorrow, but there will be another in March as well, and February has no full moon at all! Yes, there’s a name for that, too—black moon. And that’s also the name for a second new moon in a month.

Finally, the super moon—when full moon occurs near the perigee of the Moon’s orbit around Earth—happens about every 14 months, though we’re on a streak now; our December and early-January full moons were super as well. Blood moon is just a nickname for a lunar eclipse because the Moon often looks orange to deep red when totally eclipsed. None of these things, then, is unusual in and of itself, but getting them all to line up on the same day is quite a trick. The last super blue blood moon was 35 years ago (and I bet it wasn’t called that then), and the next won’t happen until 2037.

Tomorrow’s timeline

Image: NASA

For the super blue blood moon on January 31, 2018, the penumbral eclipse begins just before 3 a.m., but this is subtle and difficult to spot even with telescopes or binoculars. The real show starts just before 4 a.m., when the darker part of Earth’s shadow, the umbra, begins to work its way across the face of the Moon. The Moon will be totally eclipsed at about 4:51 a.m., and will stay that way until 6:07 a.m. The umbral eclipse will end at 7:11, and the Moon will set about 7:45.

To see it—presuming it’s not cloudy—simply go outside and look west. The Moon will be fairly high in the sky at the start of this, but closer to the horizon towards the end.

Seattle Astronomy’s Greg Scheiderer talked about the eclipse on KING 5 television today with Margaret Larson on the station’s program New Day Northwest; video of the segment is at the link in this paragraph.

The Seattle Astronomical Society plans a viewing event at Solstice Park in West Seattle for those interested in a group experience. In the event of clouds, don’t despair; NASA will be live-streaming the eclipse, though that’s never as cool as the real thing.