News Archives - Page 57 of 59

February 11, 2016March 18, 2016

Massive Planet Gone Rogue Discovered

In this artist's conception, a rogue planet drifts through space. Credit: Christine Pulliam (CfA)

A massive rogue planet has been discovered in the Beta Pictoris moving group. The planet, called PSO J318.5338-22.8603 (Sorry, I didn’t name it), is over eight times as massive as Jupiter. Because it’s one of the few directly-imaged exoplanets we know of, and is accessible for study by spectroscopy, this massive planet will be extremely important when piecing together the details of planetary formation and evolution.

Most planets outside our solar system are not directly observable. They are discovered when they transit in front of their host star. That’s how the Kepler mission finds exoplanets. After that, their properties are inferred by their gravitational interactions with their star and with any other planets in their system. We can infer a lot, and get quite detailed, but studying planets with spectroscopy is a whole other ball game.

The team of researchers, led by K. Allers of Bucknell University, used the Gemini North telescope, and its Near-Infrared Spectrograph, to find PSO’s radial and rotational velocities. As reported in a draft study on January 20th, PSO J318.5338-22.8603 (PSO from now on…) was confirmed as a member of the Beta Pictoris moving group, a group of young stars with a known age.

The Beta Pictoris moving group is a group of stars moving through space together. Since they are together, they are understood to be formed at the same time, and to have the same age. Confirming that PSO is a member of this group also confirmed PSO’s age.

Once the age of PSO was known, its identity as a planet was confirmed. Without knowing the age, it’s impossible to rule it out as a brown dwarf, a “failed star” that lacked the mass to ignite fusion.

This new rogue planet is 8.3 + or – 0.5 times the mass of Jupiter, and its temperature is about 1130 K. Spectra from the Gemini scope show that PSO rotates at between 5 to 10.2 hours, and that its radial velocity is within the envelope of values for this group. According to the researchers, determining these properties accurately means that PSO J318.5338-22.8603 is “an important benchmark for studies of young, directly imaged planets.”

PSO is in an intermediate position in terms of other planets in the Beta Pictoris moving group. 51 Eridani-b is another directly imaged planet, only slightly larger than Jupiter, discovered in 2014. The third planet in the group is Beta Pictoris b, which is thought to be almost 11 times as massive as Jupiter.

Beta Pictoris-b in orbit around the debris-disk star Beta Pictoris. Image: ESA/A-M LeGrange et. al.

Rogue, or “free-floating” planets like PSO J318.5338-22.8603 are important because they are not near a star. Light from a star dominates the star’s surroundings, and makes it difficult to discern much detail in the planets that orbit the star. Now that PSO is confirmed as a planet, rather than a brown dwarf, studying it will add to our knowledge of planetary formation.

February 11, 2016March 18, 2016

Gravitational Waves Discovered: A New Window on the Universe

An illustration of Markarian 231, a binary black hole 1.3 billion light years from Earth. Their collision generated the first gravitational waves we've ever detected. Image: NASA

“Ladies and Gentlemen, we have detected gravitational waves. We did it.”

With those words, Dave Reitze, executive director of the U.S.-based Laser Interferometry Gravitational-Wave Observatory (LIGO), has opened a new window into the universe, and ushered in a new era in space science.

Predicted over 100 years ago by Albert Einstein, gravitational waves are ripples in space-time. They travel in waves, like light does, but they aren’t radiation. They are actual perturbations in the fabric of space-time itself. The ones detected by LIGO, after over ten years of “listening”, came from a binary system of black holes over 1.3 billion light years away, called Markarian 231.

The two black holes, each 30 times as massive as the Sun, orbited each other, then spiralled together, ultimately colliding and merging together. The collision sent gravitational waves rippling through space time.

LIGO, which is actually two separate facilities separated by over 3,000 km, is a finely tuned system of lasers and sensors that can detect these tiny ripples in space-time. LIGO is so sensitive that it can detect ripples 10,000 times smaller than a proton, in laser beams 4 kilometres long.

The Laser Interferometer Gravitational-Wave Observatory (LIGO)facility in Livingston, Louisiana. The other facility is located in Hanford, Washington. Image: LIGO

Light is—or has been up until now—the only way to study objects in the universe. This includes everything from the Moon, all the way out to the most distant objects ever observed. Astronomers and astrophysicists use observatories that can see in not only visible light, but in all other parts of the electromagnetic spectrum, to study objects in the universe. And we’ve learned an awful lot. But things will change with this announcement.

“I think we’re opening a window on the universe,” Dave Reitze said.

Another member of the team that made this discovery, astrophysicist Szabolcs Marka from Columbia University, said, “Until this moment we had our eyes on the sky and we couldn’t hear the music.”

Gravitational waves are a new way to study notoriously difficult things to observe like black holes and neutron stars. Black holes emit no light at all, and their characteristics and properties are inferred from cause and effect relationships with objects near them. But the detection of gravitational waves holds the promise of answering questions about black holes, neutron stars, and even the early days of our universe, including the Big Bang.

It’s almost impossible to overstate the magnitude of this discovery. Once we understand how to better detect and observe gravitational waves, we may come to a whole new understanding of the universe, and we may look back on this day as truly ground-breaking and revolutionary.

And it all started 100 years ago with Albert Einstein’s prediction.

For a better understanding of Gravitational Waves, their sources, and their detection, check out Markus Possel’s excellent series of articles:

Gravitational Waves and How They Distort Space

Gravitational Wave Detectors and How They Work

Sources of Gravitational Waves: The Most Violent Events in the Universe

February 11, 2016March 18, 2016

NASA Says Indian Event Was Not Meteorite

Last Saturday, Feb. 6th, a meteorite reportedly struck a bus driver on the campus of the Bharathidasan Engineering College in southern India. Three students were also injured and several windows were shattered in some kind of explosion. Online videos and stills show a small crater left by the impact. If true, this would be the first time in recorded history a person was struck and killed by a meteorite.

Meteorite or …?

Call me skeptical. Since the purported meteorite weighed about 50 grams — just under two ounces — it would be far too small to cause an explosion or significant impact crater five feet deep and two feet wide as depicted in both video and still photos. There were also no reports of rumbles, sonic booms or sightings of a fireball streaking across the sky, sights and sounds associated with material substantial enough to penetrate the atmosphere and plunge to the ground. Shattered windows would indicate an explosion similar to the one that occurred over Chelyabinsk, Russia in February 2013. The blast wave spawned when the Russian meteorite fractured into thousands of pieces miles overhead pulverized thousands of windows with flying glass caused numerous injuries.

Another report of the “meteorite” fall out of India

According to a story that ran in The News Minute, a team led by the Indian Space Research Organization (IRSO) recovered an object 2 cm (3/4 inch) in width that weighed 50 grams and looked like a meteorite with “air bubbles on its rigid surface”. There’s also been chatter about meteor showers dropping meteorites to Earth, with various stories reporting that there no active meteor showers at the time of the driver’s death. For the record, not a single meteorite ever found has been linked to a shower. Dust and tiny bits of comets produce most shower meteors, which vaporize to fine soot in the atmosphere.

Now even NASA says that based on images posted online, the explosion is “land based” rather than a rock from space.

There have been close calls in the past most notably in Sylacauga, Alabama On November 30, 1954 at 2:46 p.m. an 8.5 lb rock crashed through the roof of a home not far from that town, hit a radio console, bounced off the floor and struck the hand and hip of 31-year-old Ann Hodges who was asleep on the couch at the time. She awoke in surprise and pain thinking that a space heater had blown up. But when she noticed the hole in the roof and a rock on the floor, Hodges figured the neighborhood kids had been up to no good.

Dr. Moody James shows where Ann Hodges was struck in the hip by an 8.5 lb meteorite that crashed through her roof (right). The photos appeared in the Dec. 13, 1954 issue of Life magazine. Photo by Jay Leviton, Time & Life Pictures, Getty Images

Fortunately her injuries weren’t serious. Ann became a sudden celebrity; her photo even appeared on the cover of Life magazine with a story titled “A Big Bruiser From The Sky”. In 1956 she donated the meteorite to the Alabama Museum of Natural History in Tuscaloosa, where you can still see it to this day. A second meteorite from the fall weighing 3.7 lbs. was picked up the following day by Julius K. McKinney in the middle of a dirt road. McKinney sold his fragment to the Smithsonian and used the money to purchase a small farm and used car.

Claims of people getting hit by meteorites have been on the increase in the past few years with the growth of the social media. Some stories have been deliberately made up and none have been verified. This would appear to be another tall tale if only based upon the improbabilities. In the meantime I’ve dug around and discovered another story that’s more probable and may indeed be the truth, though I have no way as of yet to independently verify it.

Police at the college say that two of the school’s gardeners were burning materials from the garden when the fire inadvertently set off sticks of dynamite that had been abandoned “amid the rocks” when the college was first built. The driver, by the name of Kamaraj and another driver, Sultan, were drinking water nearby when they were hit by the shrapnel and flying glass. Kamaraj began bleeding and was rushed to a hospital but died on the way. More HERE.

In the meantime, we only hope officials get to the bottom of the tragic death.

February 10, 2016March 18, 2016

Great Attractor Revealed? Galaxies Found Lurking Behind the Milky Way

Hundreds of galaxies hidden from sight by our own Milky Way galaxy have been studied for the first time. Though only 250 million light years away—which isn’t that far for galaxies—they have been obscured by the gas and dust of the Milky Way. These galaxies may be a tantalizing clue to the nature of The Great Attractor.

On February 9th, an international team of scientists published a paper detailing the results of their study of these galaxies using the Commonwealth Scientific and Industrial Research Organization’s (CSIRO) Parkes radio telescope, a 64 meter telescope in Australia. The ‘scope is equipped with an innovative new multi-beam receiver, which made it possible to peer through the Milky Way into the galaxies behind it.

The area around the Milky Way that is obscured to us is called the Zone of Avoidance (ZOA). This study focused on the southern portion of the ZOA, since the telescope is in Australia. (The northern portion of the ZOA is currently being studied by the Arecibo radio telescope, also equipped with the new multi-beam receiver.) The significance of their work is not that they found hundreds of new galaxies. There was no reason to suspect that galactic distribution would be any different in the ZOA than anywhere else. What’s significant is what it will tell us about The Great Attractor.

The Great Attractor is a feature of the large-scale structure of the Universe. It is drawing our Milky Way galaxy, and hundreds of thousands of other galaxies, towards it with the gravitational force of a million billion suns. The Great Attractor is an anomaly, because it deviates from our understanding of the universal expansion of the universe. “We don’t actually understand what’s causing this gravitational acceleration on the Milky Way or where it’s coming from,” said Professor Lister Staveley-Smith of The University of Western Australia, the lead author of the study.

“We know that in this region there are a few very large collections of galaxies we call clusters or superclusters, and our whole Milky Way is moving towards them at more than two million kilometres per hour.”

The core of the Milky Way seen in Infrared. Seeing through this has been a real challenge. Credit: NASA/Spitzer

Professor Staveley-Smith and his team reported that they found 883 galaxies, of which over one third have never been seen before. “The Milky Way is very beautiful of course and it’s very interesting to study our own galaxy but it completely blocks out the view of the more distant galaxies behind it,” he said.

The team identified new structures in the ZOA that could help explain the movement of The Milky Way, and other galaxies, towards The Great Attractor, at speeds of up to 200 million kilometres per hour. These include three galaxy concentrations, named NW1, NW2, and NW3, and two new clusters, named CW1 and CW2.

University of Cape Town astronomer Professor Renée Kraan-Korteweg, a member of the team who did this work, says “An average galaxy contains 100 billion stars, so finding hundreds of new galaxies hidden behind the Milky Way points to a lot of mass we didn’t know about until now.”

How exactly these new galaxies affect The Great Attractor will have to wait for further quantitative analysis in a future study, according to the paper. The data from the Arecibo scope will show us the northern hemisphere of the ZOA, which will also help build our understanding. But for now, just knowing that there are hundreds of new galaxies in our region of space sheds some light on the large-scale structure of our neighbourhood in the universe.

February 10, 2016March 18, 2016

Largest Rocky World Found

An illustration of a large, rocky planet similar to the recently discovered BD+20594b. Image: JPL-Caltech/NASA

We thought we understood how big rocky planets can get. But most of our understanding of planetary formation and solar system development has come from direct observation of our own Solar System. We simply couldn’t see any others, and we had no way of knowing how typical—or how strange—our own Solar System might be.

But thanks to the Kepler Spacecraft, and it’s ability to observe and collect data from other, distant, solar systems, we’ve found a rocky planet that’s bigger than we thought one could be. The planet, called BD+20594b, is half the diameter of Neptune, and composed entirely of rock.

The planet, whose existence was reported on January 28 at arXiv.org by astrophysicist Nestor Espinoza and his colleagues at the Pontifical Catholic University of Chile in Santiago, is over 500 light years away, in the constellation Aries.

BD+20594b is about 16 times as massive as Earth and half the diameter of Neptune. Its density is about 8 grams per cubic centimeter. It was first discovered in 2015 as it passed in between Kepler and its host star. Like a lot of discoveries, a little luck was involved. BD+20594b’s host star is exceptionally bright, which allowed more detailed observations than most exoplanets.

The discovery of BD+20594b is important for a couple of reasons: First, it shows us that there’s more going on in planetary formation than we thought. There’s more variety in planetary composition than we could’ve known from looking at our own Solar System. Second, comparing BD+20594b to other similar planets, like Kepler 10c—a previous candidate for largest rocky planet—gives astrophysicists an excellent laboratory for testing out our planet formation theories.

It also highlights the continuing importance of the Kepler mission, which started off just confirming the existence of exoplanets, and showing us how common they are. But with discoveries like this, Kepler is flexing its muscle, and starting to show us how our understanding of planetary formation is not as complete as we may have thought.

February 9, 2016March 18, 2016

New Horizons Latest Find: Floating Ice Hills On Pluto!

Ever since the New Horizons spacecraft flew by Pluto in July 2015, people here at Earth have been treated to an endless supply of discoveries about the dwarf planet. These included the first accurate pictures of what Pluto looks like, images of “Pluto’s Heart“, information about the geology and morphology of the surface (and its largest moon, Charon), and information about Pluto’s atmosphere and its escape rate.

And based on the data obtained from images by the New Horizons probe, NASA recently announced that Pluto’s flowing glaciers have numerous hills composed of water ice floating on top of them. Located in the vast ice plain known as “Sputnik Planum” – named after Sputnik One, the first satellite to orbit Earth – these hills measure several kilometers across, and are believed to be fragments that originated from the surrounding uplands.

Continue reading “New Horizons Latest Find: Floating Ice Hills On Pluto!”

February 8, 2016April 26, 2016

Peculiar ‘Cauliflower Rocks’ May Hold Clues To Ancient Mars Life

Evidence of water and a warmer, wetter climate abound on Mars, but did life ever put its stamp on the Red Planet? Rocks may hold the secret. Knobby protuberances of rock discovered by the Spirit Rover in 2008 near the rock outcrop Home Plate in Gusev Crater caught the attention of scientists back on Earth. They look like cauliflower or coral, but were these strange Martian rocks sculpted by microbes, wind or some other process?

Close-up of the lobed silica rocks on Mars photographed by the Spirit Rover on Sol 1157. Credit: NASA/ JPL-Caltech — Close-up of the lobed silica rocks on Mars photographed by the Spirit Rover’s microscopic imager on Sol 1157. It’s not known where wind (or other non-biological process) or micro-life had a hand in creating these shapes. Credit: NASA/ JPL-Caltech

When analyzed by Spirit’s mini-TES (Mini-Thermal Emission Spectrometer), they proved to be made of nearly pure silica (SiO2), a mineral that forms in hot, volcanic environments. Rainwater and snow seep into cracks in the ground and come in contact with rocks heated by magma from below. Heated to hundreds of degrees, the water becomes buoyant and rises back toward the surface, dissolving silica and other minerals along the way before depositing them around a vent or fumarole. Here on Earth, silica precipitated from water leaves a pale border around many Yellowstone National Park’s hot springs.

The Grand Prismatic Spring at Yellowstone National Park. Could it be an analog to similar springs, hydrothermal vents and geysers that may once have existed in Gusev Crater on Mars? Credit: Jim Peaco, National Park Service

Both at Yellowstone, the Taupo Volcanic Zone in New Zealand and in Iceland, heat-loving bacteria are intimately involved in creating curious bulbous and branching shapes in silica formations that strongly resemble the Martian cauliflower rocks. New research presented at the American Geophysical Union meeting last month by planetary geologist Steven Ruff and geology professor Jack Farmer, both of Arizona State University, explores the possibility that microbes might have been involved in fashioning the Martian rocks, too.

A sizzling visit to El Tatio’s geysers

The researchers ventured to the remote geyser fields of El Tatio in the Chilean Atacama Desert to study an environment that may have mimicked Gusev Crater billions of years ago when it bubbled with hydrothermal activity. One of the driest places on Earth, the Atacama’s average elevation is 13,000 feet (4 km), exposing it to considerably more UV light from the sun and extreme temperatures ranging from -13°F to 113°F (-10° to 45°C). Outside of parts of Antarctica, it’s about as close to Mars as you’ll find on Earth.

Ruff and Farmer studied silica deposits around hot springs and geysers in El Tatio and discovered forms they call “micro-digitate silica structures” similar in appearance and composition to those on Mars (Here’s a photo). The infrared spectra of the two were also a good match. They’re still analyzing the samples to determine if heat-loving microbes may have played a role in their formation, but hypothesize that the features are “micro-stromatolites” much like those found at Yellowstone and Taupo.

A stromatolite from Wyoming made of many layers of bacteria-cemented mineral grains. Credit: Bob King

Stromatolites form when a sticky film of bacteria traps and cements mineral grains to create a thin layer. Other layers form atop that one until a laminar mound or column results. The most ancient stromatolites on Earth may be about 3.5 billion years old. If Ruff finds evidence of biology in the El Tatio formations in the punishing Atacama Desert environment, it puts us one step closer to considering the possibility that ancient bacteria may have been at work on Mars.

Scientists have found evidence that Home Plate at Gusev crater on Mars is composed of debris deposited from a hydrovolcanic explosion. The finding suggests that water may have been involved in driving an eruption that formed the deposits found on Home Plate. Spirit found the silica-rich rocks at lower right near Tyrone in 2008. Credit: NASA/JPL-Caltech

Silica forms may originate with biology or from non-biological processes like wind, water and other environmental factors. Short of going there and collecting samples, there’s no way to be certain if the cauliflower rocks are imprinted with the signature of past Martian life. But at least we know of a promising place to look during a future sample return mission to the Red Planet. Indeed, according to Ruff, the Columbia Hills inside Gusev Crater he short list of potential sites for the 2020 Mars rover.

More resources:

Steve Ruff paper comparing El Tatio with an early hot springs environment in Gusev Crater
Spirit Rover raw image archive
Details about the Spirit’s discovery of silica

February 5, 2016April 26, 2016

NASA Says “No Chance” Small Asteroid Will Hit Earth On March 5th

On October 6th, 2013, the Catalina Sky Survey discovered a small asteroid which was later designated as 2013 TX68. As part Apollo group this 30 meter (100 ft) rock is one of many Near-Earth Objects (NEOs) that periodically crosses Earth’s orbit and passes close to our planet. A few years ago, it did just that, flying by our planet at a safe distance of about 2 million km (1.3 million miles).

And according to NASA’s Center for NEO Studies (CNEOS) at the Jet Propulsion Laboratory, it will be passing us again in a few weeks time, specifically between March 2nd and 6th. Of course, asteroids pass Earth by on a regular basis, and there is very rarely any cause for alarm. However, there is some anxiety about 2013 TX68’s latest flyby, mainly because its distance could be subject to some serious variation.

Continue reading “NASA Says “No Chance” Small Asteroid Will Hit Earth On March 5th”

February 5, 2016March 18, 2016

Jupiter Not the Planetary Protector We Thought it Was?

Jupiter takes a beating from Comet Shoemaker-Levy 9. Credit: NASA/Hubble Space Telescope team.

I’ve always liked the idea that Jupiter has acted like a protector to its little brother, Earth. That it has used its massive gravitational pull to divert asteroids and comets from a collision course with Earth. Maybe Jupiter even felt bad when one got through, and doomed the dinosaurs to extinction. But a new study has cast this idea into doubt.

The idea of Jupiter as a protector has been around for a while. The images of comet Shoemaker-Levy 9 breaking apart and crashing into Jupiter in 1994 reinforced the idea. But according to Kevin Grazier, at the Jet Propulstion Laboratory (JPL), rather than acting solely as a shield, re-directing comets and other objects away from the inner solar system, Jupiter may have actually directed planetesimals into the inner solar system.

Illustration of a rocky planet being bombarded by comets. (Image credit: NASA/JPL-Caltech)

In the early days of the Solar System, there was much more debris around than there is now. The early days would have been a race between planetesimals to gather enough mass to form the planets we see today. After planets were formed, there would still have been plenty of planetesimals left. This new study shows that, rather than clearing the inner solar system from all this debris that could collide with Earth, Jupiter nudged many of these planetesimals towards Earth, helping to create Earth as we know it.

As reported in January 2016 in Astrobiology, Glazier created a simulator of the solar system, and ran 30,000 particles through this simulation. All of the particles began in “non life-threatening” trajectories, but a significant number of them ended the simulation in orbits that crossed the orbit of the Earth.

So not only did Jupiter—and Saturn—re-direct material into the inner Solar System, but the simulation also showed that Jupiter slowed that material to a speed which allowed it to contribute mass to Earth.

But these planetesimals would have contributed more than just mass to Earth. They would have carried volatiles with them. Volatiles are chemical elements and molecules with low boiling points. They are associated with the atmosphere and the crust. These volatiles, which include nitrogen, hydrogen, carbon dioxide, and others, make up a large portion of the Earth’s crust. Without them, Earth would be a very different place. It may never have developed the atmosphere that has allowed life to flourish.

It’s clear that Jupiter has contributed to the evolution of Earth and the Solar System as we know it. As the largest planet by far, its influence is undeniable. As a result of this study, we better understand the dual-role Jupiter has played. While it no doubt has played the role of protector, by changing the direction of some objects on a collision course with Earth, Jupiter’s presence has also been responsible for slowing and diverting planetesimals—and their life-friendly volatiles—directly into Earth.

February 5, 2016March 18, 2016

Earth From Afar Would Look Only 82% Right For Life

From Lunar orbit, Earth is obviously habitable. But from a distant point in the galaxy, not so much. Image: NASA/LRO.

Right now, we’re staring hard at a small section of the sky, to see if we can detect any planets that may be habitable. The Kepler Spacecraft is focused on a tiny patch of sky in our Milky Way galaxy, hoping to detect planets as they transit in front of their stars. But if alien astronomers are doing the same, and detect Earth transiting in front of the Sun, how habitable would Earth appear?

You might think, because, well, here we are, that the Earth would look 100% habitable from a distant location. But that’s not the case. According to a paper from Rory Barnes and his colleagues at the University of Washington-based Virtual Planetary Laboratory, from a distant point in the galaxy, the probability of Earth being habitable might be only 82%.

Illustration of the Kepler spacecraft.(NASA/Kepler mission/Wendy Stenzel)

Barnes and his team came up with the 82% number when they worked to create a “habitability index for transiting planets,” that seeks to rank the habitability of planets based on factors like the distance from its star, the size of the planet, the nature of the star, and the behaviour of other planets in the system.

The search for habitable exo-planets is dominated by the idea of the circumstellar habitable zone—or Goldilocks Zone—a region of space where an orbiting planet is not too close to its star to boil away all the water, and not so far away that the water is all frozen. This isn’t a fixed distance; it depends on the type and size of the star. With an enormous, hot star, the Goldilocks Zone would be much further away than Earth is from the Sun, and vice-versa for a smaller, cooler star. “That was a great first step, but it doesn’t make any distinctions within the habitable zone,” says Barnes.

Comparing a star's habitable zone based on its size. Credit: Fine Art America/Detlev Van Ravenswaay — Comparing a star’s habitable zone based on its size. Credit: Fine Art America/Detlev Van Ravenswaay.

Kepler has already confirmed the existence of over 1,000 exo-planets, with over 4,700 total candidate planets. And Kepler is still in operation. When it comes time to examine these planets more closely, with the James Webb Space Telescope and other instruments, where do we start? We needed a way to rank planets for further study. Enter Barnes and his team, and their habitability index.

To rank candidates for further study, Barnes focused on not just the distance between the planet and the host star, but on the overall energy equilibrium. That takes into account not just the energy received by the planet, but the planet’s albedo—how much energy it reflects back into space. In terms of being warm enough for life, a high-albedo planet can tolerate being closer to its star, whereas a low-albedo planet can tolerate a greater distance. This equilibrium is affected in turn by the eccentricity of the planet’s orbit.

The habitability index created by Barnes—and his colleagues Victoria Meadows and Nicole Evans—is a way to enter data, including a planet’s albedo and its distance from its host star, and get a number representing the planet’s probability of being habitable. “Basically, we’ve devised a way to take all the observational data that are available and develop a prioritization scheme,” said Barnes, “so that as we move into a time when there are hundreds of targets available, we might be able to say, ‘OK, that’s the one we want to start with.’”

So where does the Earth fit into all this? If alien astronomers are creating their own probability index, at 82%, Earth is a good candidate. Maybe they’re already studying us more closely.