Orwell Astronomical Society (Ipswich)
JUICE Mission, 15 May 2023 - 11 August 2024
On 14 April 2023, the JUpiter ICy moons Explorer (JUICE) mission was launched by an Ariane 5 rocket from French Guiana. It is currently en route towards Jupiter and is due to make observations of three of the planet’s four Galilean moons, Ganymede, Europa and Callisto, during the period 2031-35.
Initially, my prospects of imaging JUICE within a few days or weeks of launch were not promising. It was cloudy over the UK on the evening of launch and then I was away from home for a while. By the time I returned home, JUICE was at a considerable distance from Earth. In addition, true darkness lasted less than two hours a night, making it difficult to image a very faint object. I therefore planned to wait for JUICE to return to the neighbourhood of Earth, during the Earth/Moon flyby in August 2024, before attempting to image it.
However, On 09 May, Milan Antoš of the Czech Republic posted an image of JUICE taken using a 250 mm scope. The following day, Nick James of Chelmford posted on the BAA forum that JUICE was much brighter than expected, at around magnitude 18. So perhaps the craft could be imaged after all...
On 15 May, the spacecraft was at a distance of 7.5 million km. It crossed the meridian in the evening nautical twilight at a declination of -4° moving at a rate of only 0.2 arcseconds per minute. I did not know if it was still at magnitude 18 but, in any case, I pressed ahead with imaging. I followed the spacecraft for 2½ hours until it started to get cloudy.
JUICE is not visible in individual 60 s exposures but can be seen in a stack of 20 minutes' worth of images. A video produced from the images shows a faint, slow-moving object very close to the location predicted by JPL Horizons. I was surprised and delighted that I was able to record a man-made object at such a vast distance. No doubt the large solar array of the craft, 85 m2 in area, helps in this regard!
August 2024 soon came around and, mid-month, the JUICE probe approached the Earth AND Moon to effect a gravity assist manoeuvre. On 19 August it will pass 700 km from the Moon then, on the evening of the next day, within 7000 km of the Earth (at 01:57 UTC on 21 August, passing over SE Asia and the Pacific Ocean.
Around mid-month, the craft was near RA 22h 30m, dec -10°, transiting around 01:00 UT, and hence visible from the UK.
I first attempt imaginging the returning probe on 10 August. I followed the predicted position of the probe from an altitude of 18° until 28°. However, the craft was not visible in any single image and I was not sure that I'd recorded it in the trailed and stacked image (because of the low altitude).
Undeterred, on 11 August, I tried again, following the predicted path from an altitude of 14° until close to transit at 28°. This time, the craft was clearly visible in the trailed and stacked images, and they confirmed that it had been visible too in the previous night's images.
The following still image, taken on 10 August, is a stack, showing the probe at a distance of some 2.8 million km. The video immediately underneath is centred by stacking frames on the probe, so field stars appear as "space-worms".
The following still image and video are as above, but taken a day later, with the probe slightly closer, at a distance of 2.5 million km.
The location of JUICE can be found from the NASA JPL Horizons ephemeris (select target body as JUICE). Up to 20 August, there are opportunities to observe the craft from the UK in the morning sky; from 21 August onwards it will be at low altitude after sunset.
Nigel Evans