Bright Explosion on the Moon
Astrophysics researchers who monitor the Moon for meteoroid impacts have detected the brightest explosion in the history of their program.
For the past 8 years, astronomers have been monitoring the Moon for signs of explosions caused by meteoroids hitting the lunar surface. Lunar meteor showers have turned out to be more common than anyone expected, with hundreds of detectable impacts occurring every year.
They've just seen the biggest explosion in the history of the program.
On March 17, 2013, an object about the size of a small boulder hit the lunar surface in Mare Imbrium. It exploded in a flash nearly 10 times as bright as anything we've ever seen before.
Anyone looking at the Moon at the moment of impact could have seen the explosion--no telescope required. For about one second, the impact site was glowing like a 4th magnitude star.
Ron Suggs, an analyst at the Marshall Space Flight Center, was the first to notice the impact in a digital video recorded by one of the monitoring program's 14-inch telescopes. It jumped right out at me, it was so bright, he recalls.
The 40 kg meteoroid measuring 0.3 to 0.4 meters wide hit the Moon traveling 56,000 mph. The resulting explosion1 packed as much punch as 5 tons of TNT.
The lunar impact might have been part of a much larger event.
On the night of March 17, University of Western Ontario all-sky cameras picked up an unusual number of deep-penetrating meteors right here on Earth. These fireballs were traveling along nearly identical orbits between Earth and the asteroid belt.
This means Earth and the Moon were pelted by meteoroids at about the same time.
"My working hypothesis is that the two events are related, and that this constitutes a short duration cluster of material encountered by the Earth-Moon system.
One of the goals of the lunar monitoring program is to identify new streams of space debris that pose a potential threat to the Earth-Moon system. The March 17th event seems to be a good candidate.
Controllers of Lunar Reconnaissance Orbiter have been notified of the strike. The crater could be as wide as 20 meters, which would make it an easy target for LRO the next time the spacecraft passes over the impact site. Comparing the size of the crater to the brightness of the flash would give researchers a valuable ground truth measurement to validate lunar impact models.
Unlike Earth, which has an atmosphere to protect it, the Moon is airless and exposed. Lunar meteors crash into the ground with fair frequency. Since the monitoring program began in 2005, astronomers associated with lunar impact has detected more than 300 strikes, most orders of magnitude fainter than the March 17th event. Statistically speaking, more than half of all lunar meteors come from known meteoroid streams such as the Perseids and Leonids. The rest are sporadic meteors--random bits of comet and asteroid debris of unknown parentage.
U.S. Space Exploration Policy eventually calls for extended astronaut stays on the lunar surface. Identifying the sources of lunar meteors and measuring their impact rates gives future lunar explorers an idea of what to expect. Is it safe to go on a moonwalk, or not? The middle of March might be a good time to stay inside.
We'll be keeping an eye out for signs of a repeat performance next year when the Earth-Moon system passes through the same region of space. "Meanwhile, our analysis of the March 17th event continues."
The Moon has no oxygen atmosphere, so how can something explode? Lunar meteors don't require oxygen or combustion to make themselves visible. They hit the ground with so much kinetic energy that even a pebble can make a crater several feet wide. The flash of light comes not from combustion but rather from the thermal glow of molten rock and hot vapors at the impact site.
Worlds Within Worlds
Astronomers have discovered an immense cloud of hydrogen evaporating from a Neptune-sized planet named GJ 436b. The planet's atmosphere is evaporating because of extreme irradiation from its parent star
Astronomers using Hubble Space Telescope have discovered an immense cloud of hydrogen evaporating from a Neptune-sized planet named GJ 436b. The planet's atmosphere is evaporating because of extreme irradiation from its parent star.
About 30 light years away, a Neptune-sized planet
is having some of its layers peeled back.
Astronomers using 's Hubble Space Telescope have discovered an immense cloud of hydrogen evaporating from a Neptune-sized planet named GJ 436b.
This cloud is spectacular. The research team has nicknamed it The 'Behemoth.'
The planet's atmosphere is evaporating because of extreme irradiation from its parent star-a process that might have been even more intense in the past.
The parent star, which is a faint red dwarf, was once more active. This means that the planet's atmosphere evaporated faster during its first billion years of existence. Overall, we estimate that the planet may have lost up to 10 percent of its atmosphere.
GJ 436b is considered to be a Warm Neptune because of its size and because it is much closer to its parent star than Neptune is to our own sun. Orbiting at a distance of less than 3 million miles, It whips around the central red dwarf in just 2.6 Earth days. For comparison, the Earth is 93 million miles from the sun and orbits it every 365.24 days.
Systems like GJ 436b could explain the existence of so-called Hot Super-Earths.
Hot Super-Earths are larger, hotter versions of our own planet. Space telescopes such as 's Kepler and the French led CoRoT have discovered hundredsof them orbiting distant stars. The existence of The Behemoth suggests that Hot Super-Earths could be the remnants of Warm Neptunes that completely lost their gaseous atmospheres to evaporation.
Finding a cloud around GJ 436b required Hubble's ultraviolet vision. Earth's atmosphere blocks most ultraviolet light so only a space telescope like Hubble could make the crucial observations.
You would not see The Behemoth in visible wavelengths because it is optically transparent. On the other hand, it is opaque to UV rays. So when you turn the ultraviolet eye of Hubble onto the system, it's really kind of a transformation because the planet turns into a monstrous thing.
The ultraviolet technique could be a game-changer in exoplanet studies, he adds. Ehrenreich expects that astronomers will find thousands of Warm Neptunes and Super-Earths in the years ahead. Astronomers will want to examine them for evidence of evaporation. Moreover, the ultraviolet technique might be able to spot the signature of oceans evaporating on Earth-like planets, shedding new light on worlds akin to our own.
Maybe you can't judge a book by its cover, but you
can judge a planet by its Behemoth.
