A Graveyard of Dead Comets

Back in the days of sailing ships, sailors found interesting areas in the world’s ocean. The Sargasso Sea was one of them. It’s a region in the North Atlantic Ocean where currents create the North Atlantic Gyre. Those currents bring in all kinds of debris, which remains stuck in the region. It’s also rich in a type of seaweed called Sargassum. Occasionally ships would get stranded there for brief periods of time due to lack of wind power to push their ships along. The Sargasso isn’t an especially deadly place, but it has been an area of great interest to marine biologists.

Our solar system has a Sargasso-like region called the Asteroid Belt, which contains a LOT of debris that has long thought to be leftovers of planetary formation that couldn’t quite get it together because of gravitational interference from Jupiter. It’s also apparently home to a lot of “dead” cometary nuclei.  This area of the solar system contains more than a million objects that range in size from a meter to more than to 800 kilometers.

A team of astronomers from the University of Antioquia, Medellin, Colombia, have examined this region of space and discovered what they call a graveyard of dead comets in the belt. Astronomer Ignacio Ferrin has just published a paper in the journal Monthly Notices of the Royal Astronomical Society, describing how what observers long thought were dead rocks in the Asteroid Belt actually turned out to be dormant comets stuck floating around out there in a solar system Sargasso.

“Dormant” means that these cometary corpses could come back to life. All they need is a Sunward nudge, and many of them would perk up as their remaining gases and ices started to sizzle again. A little push from Jupiter (via its strong gravitational pull), and the shape of any of these objects’ orbits could change, sending them closer to the Sun.

According to Ferrin and his team, the main region of the Asteroid Belt had a population of comets that formed “in situ” (meaning they formed right where they’re found) as the solar system formed. This area was once bristling with thousands of very active comets millions of years ago. As they aged and lost their outer ices, these comets began to quiet down. Ferrin’s team has studied at least 12 of these once-glorious comets that somehow got a little push toward the Sun and began fizzing again. There are very likely many more of what Professor Ferrin calls “Lazarus Comets” circling out in the Belt, just waiting for the chance to get a little closer to the Sun and get active again. Interested in learning more about how Ferrin and his team studied these comets and their implications for solar system history?  Check out their paper here or, if you’re a member of the Royal Astronomical Society, you can learn more here.

Stargazing on Vacation

I just took a few days off from cyberspace, recharging my batteries for writing. It helps a lot to step away from the keyboard and do other things—like watching sunsets. We’ve been doing it every clear night this summer. Each one is amazing, even when there are a lot of clouds in the sky. We get really dramatic sunsets, like this one.

Lately, just after sunset, the planet Venus has been putting on a show in the western twilight. You can’t miss it. It’s the bright dot of light that isn’t quite like a star. It’s going to be visible for another few weeks, so check it out.

If you wait a bit longer, you can spot Saturn in the southwestern sky. That one’s worth looking at through a small telescope if you have one handy; it’ll help you see the rings of Saturn.

After that, you just have to wait for the stars to come out.  When it’s dark enough, you can start to make out some familiar constellations.  And, if it’s really dark, you might be able to spot the Milky Way stretching across the sky.

Many stargazers use starcharts to find their way around. Many smartphone apps, such as Starmap (for iPhone) and Mobile Observatory for Android, can help you learn the constellations.  You can also download Stellarium (a free desktop planetarium program). There are many others available, so just do a search for stargazing software in your browser.

While you’re stargazing, you might see some bright flashes across the sky. In August, it usually means you’re seeing Perseid meteoroids. These are bits of space debris about the size of dust specks or grains of sand. They crash through our atmosphere and vaporize on the way in. The streak you see is a meteor. If a piece of this space stuff hits the ground, it’s then called a meteorite. Perseid meteors are bits of debris left behind by the comet Swift-Tuttle as it makes its way through its orbit. Earth’s orbit happens to pass through that cloud of dust grains in August each year. The meteors appear to come from the direction in the sky of the constellation Perseus. The shower peaks early on the morning of August 12th, but you can see its meteors for the next couple of weeks.

I always associate stargazing with summer nights for some reason. Of course, you can do it year-round, as long as you dress warmly for those winter stargazing nights. But, I guess it’s because my earliest memory of stargazing was on a warm spring night, and I just continued during the following summer. It’s a great time to start skygazing, and introduce kids to it, too!