National Astronomical Observatory of Japan

Rotating Asteroid Juno


Rotating Asteroid Juno

The asteroid Juno’s orbit lies in the space between Mars and Jupiter. It has a diameter of 240 km, making it giant for an asteroid. ALMA (Atacama Large Millimeter/submillimeter Array) observed Juno for 4 hours, taking a total of 10 photos. At this time, the distance between Juno and the Earth was approximately 300 million km, so the 0.04 arcsecond resolution achieved by ALMA corresponds to 60 km on Juno’s surface. Juno is known to rotate with a period of 7.2 hours and these 10 observational images clearly show changes in the appearance with time as the oddly shaped asteroid rotates.

A New View of Juno’s Surface

From the results of ALMA’s high angular resolution observations, we can see that Juno’s surface is not uniform. The heat capacity of the surface varies from place to place. This means it’s possible that the characteristics of the fine particles (regolith) on Juno’s surface are not homogenous.

For more details, please refer to the press release “Unprecedented views of lensed galaxy and asteroid Juno taken with ALMA.

Translation by: Ramsey Lundock (NAOJ)

Image Data

DateOctober 19, 2014
ObjectAsteroid Juno
TelescopeALMA (Atacama Large Millimeter/submillimeter Array)
Wavelength1.3 mm
InstrumentALMA Band 6


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