Planets on Our Minds


Ultraviolet images from the Hubble Space Telescope of blemishes on Jupiter, taken 2.5 hours after the impact of fragments from comet Shoemaker-Levy 9 on July21, 1994.

Credit: NASA/Hubble Space Telescope Comet Team

One recent evening, while discussing solar system aspects with students, I reviewed the spectacular collisions of comet fragments from shattered comet Shoemaker-Levy 9 that whacked Jupiter in 1994. The largest chunks, about a mile across, left explosion blemishes wider than Earth, which remained visible for many weeks amidst the huge planet’s swirling cloud tops. In July 2009, another dark spot, about 5,000 miles across, suddenly appeared on Jupiter, apparently caused by a collision with an asteroid estimated to have been a half mile wide.

Coincidentally, the morning after my SL-9 conversation, a new Jupiter close encounter was widely reported. A burst of light, probably from another asteroid impact, had been caught on video images recorded on March 17 by amateur astronomers in Austria and Ireland.

As many of you have personally seen, Jupiter is now a very bright object in our evening and early morning skies. Looking like a vivid star, but showing no hints of twinkling, we can enjoy views of that world even from light-flooded city streets throughout this spring and summer.

Making eye contact with that mega planet we remember Jupiter isn’t the only place hit hard by comets, asteroids, and meteoroids from time to time. Although Ann Hodges in Alabama was bruised when struck by an 8.5 pound meteorite that crashed through her ceiling, bounced and hit her hip in 1954, there’s no record of any person being killed by a meteorite (February reports of a such a death in India have now been discounted by NASA). However, there are at least eleven confirmed accounts of houses being hit, and in 1992 Michelle Knapp’s Chevy parked in Peekskill, New York was struck by a 26-pound stony meteorite. Perhaps you saw her red Malibu with its smashed trunk and bumper installed for a while near the American Museum of Natural History's 77th Street entrance.

For help spotting Jupiter, look up Sunday evening April 17 after twilight fades around 8:15 p.m. The planet will then be in the southeastern sky appearing about five lunar diameters from the bright gibbous Moon. The pair will subsequently progress westward until moonset at 4:35 a.m.

If you’re also in the mood for personally “catching” two other bright planets, the lunar proximity method will be helpful the night of April 24-25. Between about 11:30 p.m. and the start of morning twilight, the waning gibbous Moon appears in a triangle with nearby Saturn and Mars. Those planets are distinguished by their respective colors, yellowish-white Saturn and rusty Mars, which currently is four times brighter than the ringed giant.  We’re moving closer to Mars until the end of May when faster-orbiting Earth passes, then begins to increase our separation from the Martian orb.

Considering other planetary events: Although there won’t be another transit of Venus until 2117, when that planet next traverses the Sun’s disk when viewed from Earth, we’re looking forward to Mercury’s own solar transit on Monday May 9. It’s the first for Mercury since 2006, with the next to be in 2019, followed by a thirteen-year hiatus. Online viewing of solar transits is the safest method, unless you’re knowledgeable about use of a telescope for such observing.