Jupiter’s Disappearing Act Plus Exciting News From Vesta

Jupiter approaches conjunction with the sun in this photo taken by the SOHO's C2 coronagraph this morning. A coronagraph uses a disk to block direct sunlight. Credit: NASA/ESA

Back in the day before orbiting telescopes and 24/7 sky surveillance, when a planet got too near the sun, it was invisible in the solar glare. Not anymore. Thanks to the two coronagraphs aboard the Solar and Heliospheric Observatory (SOHO), we can follow planets right through conjunction with the sun.

SOHO is located at a stable point some 930,000 miles sunward of Earth. With no atmosphere to contend with, SOHO studies the sun from the spotless window of outer space.

Jupiter reaches solar conjunction tomorrow when it will be closest to the sun. You can see from the photo that today it’s already very close – less than one degree away or one “pinkie” finger held at arm’s length against the sky. Notice that Jupiter is a little below or south of the sun. Tomorrow it will be even closer but still travel south and miss the solar disk. Rarely do planets line up exactly with the sun during conjunction. That’s why next month’s transit of Venus is so special.

Keep in mind as you look at the picture that Jupiter lies in the distant background on the opposite side of the sun from Earth. It’s currently 558 million miles away or six times the Earth-sun distance. As you might guess, if Jupiter precisely lined up, it would be hidden behind the sun. As for that big sunspot group, it’s still lively but no X-class flares yet.

Virtual flyover of the asteroid Vesta based on hundreds of actual photographs. Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

After almost a year’s study by the orbiting Dawn space probe, NASA shared new insights about the asteroid Vesta this week. We now know that the 326-mile-diameter orb was on its way to becoming a planet 4.6 billion years ago. It developed an iron core measuring 136 miles across, a dense, rocky mantle and crust made of lava flows that were soon battered by meteorite impacts.

Bright and dark craters on Vesta. Like everything else in the solar system, the asteroid was bombarded heavily by meteorites at the dawn of the solar system. Credit: NASA/JPL-Caltech

Terrestrial planets also possess these three basic layers. With Vesta, the decay of a radioactive form of aluminum around in the early solar system generated the heat that melted the asteroid. As it cooled, heavier elements like iron and nickel sunk to form a core, while lighter elements floated to the top and solidified into the mantle and crust.

The layering, known as differentiation, make Vesta more like a small planet or Earth’s moon than most asteroids. Smaller bodies never had enough radioactive material to melt and layer-cake.

The Rheasilvia Basin dominates Vesta's southern hemisphere. The crater is 90 percent as wide as the entire asteroid. Fragments from the collision have reached Earth over the ages as HED meteorites. Credit: NASA/JPL-Caltech

By counting craters, scientists determined the age of Vesta’s biggest crater, the 314-mile-wide Rheasilvia Basin in the southern hemisphere. The impact, which removed a sizable portion of the asteroid’s southern polar region, happened only about a billion years ago, long after Vesta formed and when most meteorite bombardment had ceased

Scientists were also able to determine what minerals are in Vesta’s crust by examining how they reflect sunlight. Here’s where things really get exciting. They discovered that the meteorites in the HED clan – howardites, eucrites and diogenties – are the same materials seen in Vesta’s crust. We’ve suspected this for years because the two reflect light in almost the same way, but this is the first time we’ve visited a source of meteorites found on Earth.

A slice of Vesta! This eucrite meteorite named NWA 2724 was found in the Sahara Desert . It represents a small cross section of an ancient lava flow on the asteroid. Photo: Bob King

Eucrites are similar to lava flows on Earth; diogenites are coarse-grained crystalline rocks from the mantle and howardites are a mix of the two, created when meteorites bash, mix and cement together fragments of both crust and mantle.

It sends a chill up my spine to touch the meteorite in the photo above and know that it came directly from Vesta, launched by an impact perhaps a billion years ago. Too bad Vesta never grew larger than it is today. You can blame Jupiter. Its dominating gravitational influence stirred up material in the asteroid belt, where Vesta resides, and prevented any large body from forming.

Read more about the new Vesta results HERE.