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Emily Lakdawalla • May 17, 2010

Sighting the homeworld

Coming closer every day, Mr. Hayabusa has sighted his final destination: his homeworld, Earth, and its attendant Moon. It's not an impressive photo, because even at Hayabusa's 13-plus-million-kilometer distance from Earth, our planet is too bright, overpowering the design limits of the sensitive star tracker camera that was used to take this navigational image. What's significant about it is that Hayabusa is close enough that the camera no longer sees the Earth-Moon system as one searingly bright point of light; the star tracker now resolves ours as a double planet, a big rocky world with a big rocky companion, spinning together in space.

Sighting the home world
Sighting the home world Hayabusa's star tracker shot this photo of the Earth-Moon system on May 12, 2010, within 13.5 million kilometers of its home world. The spacecraft is aimed for a June 13 return of its sample capsule to Earth. The star tracker is designed to photograph stars, so targets as bright as the Moon and Earth are overpoweringly bright. Neither body actually subtends more than one pixel; their apparent size results from their bright points of light spilling over into adjacent pixels. However, the star tracker successfully separates the light of the Moon and Earth, resolving them as distinct points of bright light.Image: JAXA / ISAS

Here's some more detailed information provided by JAXA about the viewing geometry and background stars in this photo.

Imaging geometry for Hayabusa's May 12, 2010 photo of Earth
Imaging geometry for Hayabusa's May 12, 2010 photo of Earth Image: ISAS / JAXA

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