Ray Of Sunshine On A Dark Day

Mercury, the smallest planet, and Jupiter, the largest, are closest tonight in the western sky during twilight. Created with Stellarium

Don’t forget. Tonight Mercury and Jupiter will be at their closest low in the western sky starting about 35 minutes after sunset. Last night I managed to see and photograph the pair just in time before they were lost in the clouds. Both planets were surprisingly easy to spot.

Jupiter and Mercury last night before they were swallowed by clouds. Photo: Bob King

Find brighter Jupiter first – which tonight will be a bit lower in the sky than Mercury – and then look to its upper right see Mercury. Jupiter is dropping lower in the west every day and will soon disappear in the solar glow, while Mercury continues to hang in there for nearly two more weeks.

The next few evenings are best for finding the elusive inner planet thanks to Jupiter being nearby.

Japan’s tsunami, earthquake and damaged nuclear reactors have dominated the news over the past week. Nearly lost among these stories are the rays of light still shining from the Japanese mission to asteroid 25143 Itokawa. The journey, which unfolded between 2005 and 2010, was fraught with problems ranging from a solar flare that early on damaged the ship’s solar panels to computer and equipment malfunctions. Then things got worse.

The asteroid 25143 Itokawa is 1,755 feet long and orbits in the vicinity of Earth and Mars. Instead of solid rock, it's a loose pile of rubble. Credit: JAXA

In 2005, the Hayabusa spacecraft attempted twice to sample the surface of the rocky rubble asteroid Itokawa by firing a projectile at the surface at close range and collecting bits of flying rocks and debris into a funnel inside the ship.

During both attempts, the projectile failed to fire.

Later it was determined that during one of the firings, Hayabusa actually landed on the surface for half an hour. Mission planners hoped that during contact with the surface, it might have picked up dust grains from the asteroid. When the sample capsule landed back on Earth, Japanese scientists were elated at finding more than 1,500 asteroid dust particles inside.

A dust grain about the thickness of a human hair collected from the asteroid Itokawa. Several minerals are identified. Credit: JASA

These things are tiny. A few are 100 microns in diameter or about the width of a human hair, while most are a tenth that size. Turns out that’s plenty big enough to analyze. A preliminary analysis released earlier this week revealed that Itokawa’s dust looks a lot like stony meteorites that regularly fall to Earth. The grains are composed of olivine, plagioclase and other minerals routinely found in meteorites. And they’re just as ancient, having formed during the genesis of the solar system 4.6 billion years ago.

Their closest match are the LL chondrites, stony meteorites both low in total iron and low in free metal, the shiny flecks you see when you cut one open.

The Ragland meteorite is an LL chondrite found in 1982 in New Mexico . It's related to dust retrieved from Itokawa. Credit: Claire H.

Astronomers have long suspected that the meteorites in our collections hark from collisions between asteroids that sent fusillades of fragments flying hither and yon across the solar system. Some of these survived atmospheric entry and landed on Earth.

In spite of the Hayabusa mission’s many setbacks, samples from an asteroid – the first ever – were safely returned to Earth.  We hope that same spirit of taking a bad thing and turning it around will help the Japanese people during their recovery from the terrors of recent days. Our thoughts are with them.

2 Responses

  1. Mike

    Good morning Bob!
    Saw both Jupiter and Mercury last night. Thanks for the heads up! I sent you a photo I did of the aurora on Rainy Lake on TH night last week; did you get that? I was wondering if you could suggest what I could have done to make it better. Thanks Bob!

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