Being number two isn’t all that bad. Less pressure than the number one spot and yet you still have a foot in the limelight. Asteroid 2 Pallas was the second asteroid discovered back in the days when asteroids were so few and novel they were called planets. German astronomer Heinrich Olbers accidentally ran across it while attempting to find another asteroid, Ceres, on March 28, 1802.
This week you can see Pallas at its brightest in two decades as it treks from Sextans into Hydra the Water Snake during convenient evening viewing hours. With the asteroid shining at around magnitude 7 – just one level fainter than naked eye visibility – all you need is a pair of binoculars, a map and a clear night.
At 338 miles across, Pallas bests Vesta in size by just 12 miles, making it the second largest asteroid after Ceres, the only main belt asteroid also classified as a dwarf planet. Unlike the planets, Pallas orbits the sun in a highly inclined orbit (34.8 degrees) taking 4.6 years to complete one spin around the sun. Pallas’ average distance from the sun is 257 million miles, but this month it’s lined up favorably with Earth and only about 115 million miles away. It was last this bright in 1991 and won’t be again until 2028.
Being so much smaller than any of the eight planets, Pallas looks exactly like a star through most telescopes. Even the orbiting Hubble Space Telescope, located far above the blurring effects of Earth’s turbulent atmosphere, sees the asteroid as a pixelated object the shape of a flattened sphere with a large, darker “depression” that might be a crater.
Don’t expect a mission to the #2 anytime soon; Pallas’ highly tilted orbit makes it extremely difficult, energy and time-wise, to dispatch a probe for in-depth study and photo-taking.
That hasn’t stopped astronomers from eking out what they can across the millions of miles that separate us. Pallas receives light from the sun, absorbing some and reflecting the rest back into space. Rocks absorb light according to their internal makeup, imprinting their mineral signatures in the light they reflect back into space. Different rocks, different imprints.
Examining Pallas’ light with a spectrograph, which can dissect light like a doctor working a scalpel, we can identify basic minerals on the asteroid’s surface. From these observations, astronomers have learned that Pallas has much in common with the CR group of carbonaceous chondrite meteorites, both of which are very ancient and contain water and carbon.
This week Pallas will be near Alphard, an orange-tinted star and the brightest in Hydra, making it easy to find. It rides high in the southeastern sky around 9 p.m. local time. At magnitude 2 (Big Dipper brightness), Alphard stands out in a rather empty region of sky. You can find it by reaching your balled fist to Regulus in Leo and looking a little more than a fist below and to its right. Or you can do the same with Procyon in Canis Minor and look below and left.
Next, focus your binoculars on Alphard and use the map to stepping-stone your way to Pallas. The fun begins when you observe the asteroid for a second or third time and watch it move among the stars pulled by the gentle tug of the sun’s gravity.