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A big rock for my anniversary

—CHARLIE CHRISTMANN
It just so happens that my wedding anniversary is April 13. So, for our 44th anniversary, I plan to give my wife what she has been asking for—a great big rock. It was a Popular Mechanics magazine article from December last year that put me in the mood to investigate this timely gift to my wife.

Actually, our 44th anniversary is not until 2029, so I have some time here. And, the big rock I’m planning won’t be on her finger, it will be in the sky. The rock is 99942 Apophis, and it will be passing by Earth on lucky Friday the 13th, 2029. 99942 Apophis is a large one-thousand-foot wide, twenty-five million ton piece of leftover space debris from the formation of our solar system. Its relative motion to Earth has it passing us at around twenty-eight thousand miles per hour as it orbits the Sun every 323 days.

I say lucky, because when this asteroid was discovered on June 19, 2004, by a team from the NASA-funded University of Hawaii Asteroid Survey at Kitt Peak National Observatory in Arizona, the preliminary predictions looked dire for us. There was a very strong chance that this asteroid, two-thirds the size of Wyoming’s Devil’s Tower, would impact the Earth on that fateful Friday. In fact, the risk briefly reached level 2 out of a possible 10 on the Torino Scale (10 is the lowest chance; 1 is almost certain).

99942 Apophis is large enough to wipe out a small country were it to hit solid ground, yielding enough explosive force to equal sixty-five thousand Hiroshima bombs. If it hit the oceans, a tsunami more than eight hundred feet high would inundate many coastal areas. This asteroid is larger than the asteroid that carved Meteor Crater in Arizona thousands of years ago, and much bigger than one that exploded in the air above Siberia in 1908, flattening thousands of square miles of forest.

Thankfully, after searching for and finding several sightings in previous sky surveys of 99942 Apophis, made before its official discovery, and making new observations, the probability of a collision with us or our Moon dropped to 1-in-300 by December 2004. Subsequent measurements predict a razor-thin shave on April 13, 2029, but no collision. That thin margin will be somewhere between eighteen thousand and twenty-one thousand miles from the surface of Earth. This rock will take a path well inside the Moon’s orbit (two hundred thirty-nine thousand miles) and closer to us than many orbiting man-made satellites (up to twenty-two thousand miles). The International Space Station is safe, as it orbits at two hundred-fifty miles up.

As the asteroid passes us in 2029, it will be a first in modern history. Those in Europe, Africa, and western Asia, who will see the asteroid, can expect to see a fast-moving star at magnitude 3.3 passing through the constellation of Cancer. That would be easily visible under dark skies without the help of binoculars or telescopes. The only other visible asteroid is Vesta, 334 miles in diameter, orbiting in the main asteroid belt between Mars and Jupiter. It periodically gets as bright as magnitude 5.3, which is visible to the naked eye under a very dark sky.

Our close encounter with 99942 Apophis may not be over, according to some doomsday predictors. According to calculations, if 99942 Apophis precisely hits a ìkeyholeî distance from Earth in 2029 of 18,893 miles, the asteroid will be back for another, much less friendly visit exactly seven years later on April 13, 2036. This time the target would be somewhere along a line from Russia through the Pacific, across Central America and into the Atlantic. Not the best present for my 51st anniversary. NASA has placed the probability of this scenario happening at around 45,000-to-1.

As of the end of March this year, 853 potentially hazardous asteroids have been discovered. On March 11, 2007, asteroid 2007EH passed 119,500 miles from us, and 2007EK missed by 16,700 miles. Both were inside the Moon’s orbit. Still other future close shaves are scheduled for November 2011 by 2005 YU55 at ninety-nine thousand miles, 2001 WN5 in June 2028 at one hundred fifty-five thousand miles. But none of the 853 known asteroids that pass close to us are expected to impact us through the year 2178.

THE PLANETS AND THE MOON
• Mercury will be rising in the east after sunrise this month.
• Venus will set in the western sky from 10:30 p.m. early in the month to 11:15 p.m. later in the month. Venus will join the Moon in a close encounter on the 19th.
• Mars is an early morning riser in the east about 4:45 a.m. Look for a Mars—Moon conjunction on the 14th.
• Jupiter rises around 1 a.m. early in April and 11 a.m. late in the month. Check out the Jupiter—Moon conjunction near the star Antares, in Scorpius, one hour before sunrise on the 8th.
• Saturn is up at sunset and will set in the west between 11 p.m. and 3 a.m. through the month. On the 24th, an hour after sunset, look for a conjunction between the Moon and Saturn, above the western horizon. To the left of Saturn will be the star Regulus. To the right of the Moon will be Pollux and Castor, the Gemini twins. Bright Sirius will be low, below the twins. Procyon is a bit above Sirius.
• The Moon is full on April 2. Easter is the first Sunday after the first Full Moon of Spring, making it April 8th this year. The New Moon is on the 17th, when the Moon reaches perigee at 221,914 miles, its closest approach to Earth. The Moon’s apogee is on the 3rd, the farthest from Earth, at 252,479 miles.

If you have a question or comment for Charlie, you may email him at k5cec@yahoo.com.