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Artist's view of plumes on Europa (right) // NASA
Artist's view of plumes on Europa (right) // NASA

Plumes on Europa May Enable the Hunt for Alien Life

Artist's view of plumes on Europa (right) // NASA
Artist's view of plumes on Europa (right) // NASA

Jupiter’s moon Europa likely has water plumes—great geysers of saline ocean blasting from its icy shell. That's what scientists announced earlier today, reaffirming previous observations of plume activity on the Galilean moon. The findings raise the stakes for the agency's next flagship planetary mission, slated to launch for Europa around 2022.

The plumes, which are estimated to rise 125 miles above Europa's surface, were captured using the Hubble Space Telescope, NASA's 26-year-old space-based orbiting observatory. "We are working at the limits of Hubble's unique capabilities," said William Sparks, an astronomer with the Space Telescope Science Institute, during a press teleconference. To find the plumes, scientists used what’s known as transit imaging operations, observing the silhouette of Europa against the bright surface of Jupiter. It took 50 million observation events to generate the plume images, which were carefully processed through specially designed software.

NASA teased the results last week, promising "surprising activity" on the moon. Plumes fit the bill, and have implications beyond celestial wonder and geologic thrill-seeking. Europa is an ocean world, and is thought to have all of the ingredients necessary for life. Though it is only about the size of our own moon, it hosts a saltwater ocean with twice the water of Earth's oceans. That water is sandwiched between an ice shell and a rocky mantle. When water touches rock, interesting chemical processes result—especially if there are hydrothermal vents from the planet's interior blasting hot water into the ocean. The conditions for life on Europa are at least as hospitable as what can be found in the deepest parts of Earth's ocean. The plumes help kick open the door for alien, Europan creatures, though what we might find there remains a mystery.

The problem has always been getting to Europa’s ocean to take a sample. The ice shell is likely many miles thick—beyond the drilling capacity even here on Earth. Plumes solve that problem. We don't need to go to the ocean; we can have the ocean come to us. The Europa Multiple Flyby Mission in development by NASA will see a spacecraft enter orbit around Jupiter, circling the gas giant hundreds of times. Each time it comes around to Europa, it will scan and image the icy world. This technique, rather than a direct Europa orbiter, allows the spacecraft to avoid the worst of the punishing radiation belt in the Jovian environment. Scientists can now plan trajectories that allow the spacecraft to fly through the plumes in order to analyze their composition.

However, nobody is promising life detection yet. The multiple flyby mission is designed to study habitability. Follow-up missions—likely Europa landers—would actually determine the life question. (The plumes help a lander as much as they do a flyby, since water that blasts from Europa's shell would rain back down to the surface. A lander could make extraordinary observations by drilling only a few inches down.) Lander concepts are currently under development at Jet Propulsion Laboratory in southern California. The multiple flyby spacecraft is being developed jointly by JPL and the Johns Hopkins University Applied Physics Laboratory in Maryland.

"For a long time, humanity's been wondering whether there is life beyond Earth," said Paul Hertz, director of the astrophysics division at NASA headquarters. "We're lucky to live in an era when we can address such evidence scientifically."

For now, the discovery could only have been made with the sensitivity of the Hubble. "Hubble is the only telescope that we have right now capable of observing Jupiter and Europa at this detail in ultraviolet light," said Jennifer Wiseman, senior Hubble project scientist at NASA's Goddard Space Flight Center. The space telescope's science mission was recently extended by five years, until 2021, at which time NASA will have to decide whether to keep the space telescope operational. The powerful James Webb Space Telescope, Hubble's successor, is slated to launch in 2018. "We're particularly excited about using the James Webb Space Telescope ... to look for additional evidence of Europa water,” Wiseman says.

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Scott Butner, Flickr // CC BY-NC-ND 2.0
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Space
Look Up! The Lyrid Meteor Shower Arrives Saturday Night
Scott Butner, Flickr // CC BY-NC-ND 2.0
Scott Butner, Flickr // CC BY-NC-ND 2.0

There is a thin line between Saturday night and Sunday morning, but this weekend, look up and you might see several of them. Between 11:59 p.m. on April 21 and dawn on Sunday, April 22, the Lyrid meteor shower will peak over the Northern Hemisphere. Make some time for the celestial show and you'll see a shooting star streaking across the night sky every few minutes. Here is everything you need to know.

WHAT IS THE LYRID METEOR SHOWER?

Every 415.5 years, the comet Thatcher circles the Sun in a highly eccentric orbit shaped almost like a cat's eye. At its farthest from the Sun, it's billions of miles from Pluto; at its nearest, it swings between the Earth and Mars. (The last time it was near the Earth was in 1861, and it won't be that close again until 2280.) That's quite a journey, and more pressingly, quite a variation in temperature. The closer it gets to the Sun, the more debris it sheds. That debris is what you're seeing when you see a meteor shower: dust-sized particles slamming into the Earth's atmosphere at tens of thousands of miles per hour. In a competition between the two, the Earth is going to win, and "shooting stars" are the result of energy released as the particles are vaporized.

The comet was spotted on April 4, 1861 by A.E. Thatcher, an amateur skywatcher in New York City, earning him kudos from the noted astronomer Sir John Herschel. Clues to the comet's discovery are in its astronomical designation, C/1861 G1. The "C" means it's a long-period comet with an orbit of more than 200 years; "G" stands for the first half of April, and the "1" indicates it was the first comet discovered in that timeframe.

Sightings of the Lyrid meteor shower—named after Lyra, the constellation it appears to originate from—are much older; the first record dates to 7th-century BCE China.

HOW CAN I SEE IT?

Saturday night marks a first quarter Moon (visually half the Moon), which by midnight will have set below the horizon, so it won't wash out the night sky. That's great news—you can expect to see 20 meteors per hour. You're going to need to get away from local light pollution and find truly dark skies, and to completely avoid smartphones, flashlights, car headlights, or dome lights. The goal is to let your eyes adjust totally to the darkness: Find your viewing area, lay out your blanket, lay down, look up, and wait. In an hour, you'll be able to see the night sky with great—and if you've never done this before, surprising—clarity. Don't touch the smartphone or you'll undo all your hard ocular work.

Where is the nearest dark sky to where you live? You can find out on the Dark Site Finder map. And because the shower peaks on a Saturday night, your local astronomy club is very likely going to have an event to celebrate the Lyrids. Looking for a local club? Sky & Telescope has you covered.

WHAT ELSE IS GOING ON UP THERE?

You don't need a telescope to see a meteor shower, but if you bring one, aim it south to find Jupiter. It's the bright, unblinking spot in the sky. With a telescope, you should be able to make out its stripes. Those five stars surrounding it are the constellation Libra. You'll notice also four tiny points of light nearby. Those are the Galilean moons: Io, Europa, Ganymede, and Callisto. When Galileo discovered those moons in 1610, he was able to prove the Copernican model of heliocentricity: that the Earth goes around the Sun.

THERE'S BAD WEATHER HERE! WHAT DO I DO?

First: Don't panic. The shower peaks on the early morning of the 22nd. But it doesn't end that day. You can try again on the 23rd and 24th, though the numbers of meteors will likely diminish. The Lyrids will be back next year, and the year after, and so on. But if you are eager for another show, on May 6, the Eta Aquariids will be at their strongest. The night sky always delivers.

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Space
New NASA Satellite Called TESS Could Discover Thousands of New Planets

Since NASA’s Kepler spacecraft launched in 2009, the space agency has found and confirmed a whopping 2343 new planets. Of those, 30 are considered to be situated in a “habitable zone,” an area in which a planet’s surface could theoretically contain water.

A new satellite, set to launch today, is expected to find thousands more planets outside of our solar system, known as exoplanets. TESS, short for the Transiting Exoplanet Survey Satellite, is NASA’s latest effort to plumb the depths and darkness of outer space in search of other Earth-like planets—including those that could potentially support life.

TESS is slated to complete a two-year survey of the “solar neighborhood,” a general region which comprises more than 200,000 of the brightest nearby stars. To find these outlier planets, NASA scientists will be keeping an eye out for temporary changes in brightness, which indicate that a planet is blocking its host star.

According to Martin Still, the program scientist working on the TESS mission, the launch comes “with certainty” that TESS will find many nearby exoplanets. "We expect to find a whole range of planet sizes, between planets the size of Mercury or even the Moon—our Moon—to planets the same size as Jupiter and everything in between,” Still said in a NASA interview.

While the Kepler mission was considered a major success, NASA noted that most of the planets it recorded are those that orbit faint, faraway stars, making it difficult to conduct follow-up observations. The stars that TESS plans to survey will be 30 to 100 times brighter than those observed by its predecessor. This allows for newly detected planets and their atmospheres to be characterized more easily.

“Before Kepler launched, we didn't know for sure if Earth-sized planets existed,” Elisa V. Quintana, a NASA astrophysicist, told Reddit. “Kepler was a statistical survey that looked at a small patch of sky for four years and taught us that Earths are everywhere. TESS is building on Kepler in the sense that TESS wants to find more small planets but ones that orbit nearby, bright stars. These types of planets that are close to us are much more easy to study, and we can measure their masses from telescopes here on Earth.”

The most common categories of exoplanets are Earth- and Super Earth–sized masses—the latter of which are larger than Earth but smaller than Uranus and Neptune.

TESS is scheduled to launch from the Cape Canaveral Air Force Station in Florida on a SpaceX Falcon 9 rocket at 6:32pm EDT today.

For more information about TESS, check out this video from NASA.

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