Methane is often produced by living things, and it doesn’t persist long in atmospheres because it is quickly broken down by solar radiation. Yet satellites and rovers have periodically detected surges in atmospheric methane concentration on Mars, raising the question: where is that gas coming from?
Methane gas periodically wafts into the atmosphere of Mars; that notion, once considered implausible and perplexing, is now widely accepted by planetary scientists. […]
The presence of methane is significant because the gas decays quickly. Calculations indicate that sunlight and chemical reactions in the thin Martian atmosphere would break up the molecules within a few hundred years, so any methane detected must have been created recently.
It might have been created by a geological process known as serpentinization, which requires both heat and liquid water. Or it could be a product of life — specifically methanogens, microbes that release methane as a waste product. Methanogens thrive in places lacking oxygen, such as rocks deep underground and the digestive tracts of animals.
Even if the source of the methane turns out to be geological, the hydrothermal systems that produce the emissions would still be prime locations to search for signs of life.
On February 6, the largest meteor impact since the 2013 Chelyabinsk incident occurred over the southern Atlantic Ocean, yielding a fireball with an explosive force greater than 13,000 tons of TNT (13 kt) — a blast at least as energetic as the Hiroshima bomb. (By comparison, the Chelyabinsk meteor exploded over Russia with a force equal to 440,000 tons of TNT.)
Don’t worry too much, though — this headline is somewhat sensationalist. In fact, NASA keeps track of meteor impacts like this one, and it turns out that they occur on a fairly regular basis, with airbursts of this size happening every five to ten years or so, on average. To put this in a little more context, there have been six impact events during the past ten years equal or greater in size to the February 6 incident. Over this period, NASA has recorded a total of 292 meteor airbursts that have had an explosive force greater than 73 tons of TNT. (The median blast had a force equal to 230 tons of TNT.)
Unfortunately, since the February 6 event occurred in the middle of the ocean, no one was around to capture video footage of what was surely a visually-striking fireball. (Data on the February 6 event, iflscience.com reports, “were given to NASA by the U.S. government. Detecting atmospheric explosions is most likely a high priority of several branches of the U.S. military, so a fireball of such magnitude could have been easily picked up. Satellite imagery and infrasound atmospheric microphones could both be used to detect an impact like this.”)
The Chelyabinsk meteor, on the other hand, exploded over a fairly populated region and consequently was caught on film from multiple angles (you can check out some video footage of that event below). Because the Chelyabinsk meteor exploded so high in the atmosphere (at an altitude of 18.4 miles), it did little damage beyond shattering windows and scaring the bejeezus out of everyone in range.
The last meteor to inflict massive damage on the ground was the Tunguska impacter, which completely flattened 770 square miles of Siberian forest back in 1908. That meteor had a destructive force of at least 15 megatons — 1,000 times more powerful than the Hiroshima bomb.
Whenever these events happen, of course, the first question on everyone’s mind is something along the lines of, “would we be ready if a bigger one was headed our way?” The answer to this is “probably not.” However, don’t let it concern you too much — the chances of a life-threatening impact occurring during our lifetimes is infinitesimally small, and we’ve got plenty of eyes on the sky that would spot such an object well in advance.