ESA/Rosetta/NAVCAM via Flickr // CC BY-SA IGO 3.0
ESA/Rosetta/NAVCAM via Flickr // CC BY-SA IGO 3.0

Scientists Discover Oxygen in a Comet

ESA/Rosetta/NAVCAM via Flickr // CC BY-SA IGO 3.0
ESA/Rosetta/NAVCAM via Flickr // CC BY-SA IGO 3.0

The comet 67P/Churyumov–Gerasimenko made history just under a year ago when the European Space Agency landed the Philae probe on its surface—the first time we’ve ever landed a probe on a comet nucleus. Unfortunately, it bounced when it landed, greatly complicating the mission. 

Now scientists using instruments aboard the Rosetta spacecraft, which orbits the comet and deployed Philae, have discovered molecular oxygen in the coma of the comet, as they describe in a study published today in Nature. The oxygen was detected in the coma, or cloud of gas, surrounding the nucleus of the comet. This the first time oxygen has been discovered in a cometary coma.

Rosetta has detected an abundance of different gases pouring from the comet's nucleus, primarily water vapor, carbon monoxide, and carbon dioxide. Surprisingly, the fourth-most abundant material was molecular oxygen, relative to water. “It’s not only that we have oxygen—we have a lot of oxygen,” the University of Bern’s Kathrin Altwegg, a co-author on the paper, said in a press teleconference on Tuesday.

Using more than 3000 samples gathered from September 2014 to March 2015 by the ROSINA mass spectrometer aboard Rosetta—which began circling the comet in May 2014 after a 10-year journey—Altwegg, a principal investigator on the instrument, and her colleagues detected oxygen embedded in icy grains. It accounts for on average about 3.8 percent of the material, relative to water, in the comet’s coma. (The amount of molecular oxygen detected showed a strong relationship to the amount of water measured at any given time, suggesting that their origin on the nucleus and release mechanism are linked, the ESA said in a statement.)

The finding is surprising because oxygen, the third-most abundant element in the universe, is highly chemically reactive; it likes to combine with other chemicals. It was previously thought that in the early solar system it must have combined with the abundant hydrogen then present to form water. The oxygen molecules in the comet perhaps tell a different story. “We had never thought that oxygen could ‘survive’ for billions of years without combining with other substances,” Altwegg said in a statement.

The researchers say the finding may help illuminate the chemistry of the formation of our solar system. Comets are the most primitive bodies in our solar system, forming in its outer reaches some 4.6 billion years ago, as the planets were still forming. Usually, about 95 percent of the total gas density in the comas of comets is composed of hydrogen dioxide, carbon monoxide, and carbon dioxide. Sulfuric compounds and complex hydrocarbons have been discovered on comets too. But molecular oxygen has never been detected on a comet before. It’s only been found on other icy bodies like the moons of Jupiter and Saturn.

Another instrument aboard Rosetta appears to have found oxygen too. The ALICE far-ultraviolet spectrograph may have also detected molecular oxygen spectroscopically in 67P, according to Paul Feldman, a co-investigator on ALICE.

“The work is a tour de force of mass spectrometry and a very welcome result,” Feldman told mental_floss. “It supports our inference from far-ultraviolet spectroscopy of the presence of O2 as one of the volatile drivers of cometary activity.” The ALICE findings will be published soon in a special issue of the journal Astronomy and Astrophysics devoted to the Rosetta mission.

Nicolas Biver is a co-investigator on Rosetta's MIRO, a microwave instrument that senses temperature and can identify chemicals. Last week he published a study in Science Advances detailing how the comet Lovejoy is spewing a cocktail-ready mix of alcohol and sugar into space. He wasn't involved in the oxygen study but alerted to it by his Rosetta colleagues. 

“We were not expecting to find much O2 in the cometary nuclei,” Biver told mental_floss. “We need to measure the abundance of O2 in other comets to confirm this discovery—and also because each technique can have its own bias, but this will not be easy as O2 is difficult to observe remotely (and impossible from the ground).”

As Altwegg explained, that’s because oxygen is difficult to observe from telescopes using spectroscopy. Nevertheless, she suspects it might be quite common in comets. The team is looking at Halley's comet right now for comparison. That research is ongoing.

This discovery could complicate our search for life in the universe. While oxygen and methane are considered biosignatures of life on Earth, their presence in the comet suggests we may need to rethink that idea. “If we look at exoplanets, our goal, of course, will be to detect biosignatures, to see if the planet contains life," Altwegg said. "And as far as I know, so far the combination of methane and O2 was a hint that you have life underneath it. On the comet, we have both methane and O2, but we don’t have life. So it’s probably not a very good biosignature.”

Scott Butner, Flickr // CC BY-NC-ND 2.0
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.


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.


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.


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.


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.

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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