Breaking Up is Hard to Do

Mars is finally getting close enough to show some detail as it draws nearer to its opposition at the end of the year. By late October its apparent size grows to a bit over 11” (that’s arc seconds, not inches). That’s still not large, but it’s big enough that a determined late-night observer can start picking out major surface features like the poles, Syrtis Major and Hellas. Look for the phase, too: it’ll be noticeably gibbous.

Unfortunately, it’s a very late evening object throughout the month. Even by the end of October Mars doesn’t rise until just before 10pm, so it’s not a good bet if you like to set up a telescope on Halloween for the trick- or-treaters. Halloween presents a puzzle this year. Most years, it’s dark enough to show anything in the sky by the time the kids come calling, because we’ve already switched from Daylight Savings Time back to standard time. But this year, thanks to the Energy Policy Act of 2005, we’ll stay on Daylight Savings Time through the first weekend in November, so the little witches and warlocks may start coming by while the sky is still light.

The gibbous near-third-quarter moon won’t help much either - it rises even later than Mars. For early trick-or-treaters, Jupiter is your best bet: it sets early (around 8:20) but if you have a good western horizon, even down low Jupiter can be impressive to folks who haven’t looked through a telescope before. Once it sets, you could try Uranus: it’s well up by sunset, and its pale green disk might impress some trick- or-treaters. Neptune, too, is up and visible in the early evening sky.

Pluto, obviously not a good trick-or-treater showpiece, isn’t a great target for anyone this month, since it starts the evening low in the sky and sets early. The rest of the planets are up in the morning: Venus, Saturn, and low, fleeting Mercury.

If you get up early to look at those planets, mid to late October is a good time to watch for the morning zodiacal light. Look to the east just before the sky begins to brighten. The faint glow comes from tiny particles following the plane of the ecliptic, left over from the dust of the early solar system. It’s a band of light reaching up from the horizon along the ecliptic, past Venus, Saturn and the star Regulus.

Speaking of the early solar system, did you hear the news last month about the Baptistina Breakup? No, not a band: a big asteroid. A recent study of asteroid (298) Baptistina suggests that it’s actually just a piece of a much larger 170 km asteroid. This parent asteroid broke up long ago - probably due to a collision with another asteroid - creating a swarm of asteroids now called the Baptistina family.

The team publishing in Nature ran computer simulations on the orbits of the currently known Baptistinas. They think the breakup occurred roughly 160 million years ago, in the mid-Jurassic. Most of the fragments stayed in the asteroid belt, but a few of them wandered gradually in toward the inner planets; and almost 100 million years later, one of the fragments from the breakup smacked down near the modern-day Yucatan peninsula as the Chicxulub meteor, the impact that most likely wiped out the dinosaurs.

But besides being interesting, does this have anything to do with shallow sky observing? Right now, (298) Baptistina itself isn’t much to look at. It’s 15th magnitude and sitting in the belly of Leo, rising at about 4am.

But it turns out there’s another member of the Baptistina family whose effects you’ve seen many times. The research team thinks that some 45 million years before that Chicxulub impact, another piece from the same parent asteroid smacked into the moon - to become the crater Tycho, with its huge ray system that’s so prominent when the moon is full.

So if you find yourself looking at the full moon around the end of this month, or if any little dinosaurs come to your door on the 31st demanding candy, give a thought to little (298) Baptistina ... sister to the asteroid that killed the dinosaurs and gave us mammals a chance.