5.3 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| 486958 Arrokoth | 7/8 | https://en.wikipedia.org/wiki/486958_Arrokoth | reference | science, encyclopedia | 2026-05-05T13:09:12.451441+00:00 | kb-cron |
In June and July 2017, Arrokoth occulted three background stars. The team behind New Horizons formed a specialized "KBO Chasers" team led by Marc Buie to observe these stellar occultations from South America, Africa, and the Pacific Ocean. On 3 June 2017, two teams of NASA scientists tried to detect the shadow of Arrokoth from Argentina and South Africa. When they found that none of their telescopes had observed the object's shadow, it was initially speculated that Arrokoth might be neither as large nor as dark as previously expected, and that it might be highly reflective or even a swarm. Additional data taken with the Hubble Space Telescope in June and July 2017 revealed that the telescopes had been placed in the wrong location, and that these estimations were incorrect. On 10 July 2017, the airborne telescope SOFIA was successfully placed close to the predicted centerline for the second occultation while flying over the Pacific Ocean from Christchurch, New Zealand. The main purpose of those observations was the search for hazardous material like rings or dust near Arrokoth that could threaten the New Horizons spacecraft during its flyby in 2019. Data collection was successful. A preliminary analysis suggested that the central shadow was missed; only in January 2018 was it realized that SOFIA had indeed observed a very brief dip from the central shadow. The data collected by SOFIA will also be valuable to put constraints on dust near Arrokoth. Detailed results of the search for hazardous material were presented on the 49th Meeting of the AAS Division for Planetary Sciences, on 20 October 2017. On 17 July 2017, the Hubble Space Telescope was used to check for debris around Arrokoth, setting constraints on rings and debris within the Hill sphere of Arrokoth at distances of up to 75,000 km (47,000 mi) from the main body. For the third and final occultation, team members set up another ground-based "fence line" of 24 mobile telescopes along the predicted ground track of the occultation shadow in southern Argentina (Chubut and Santa Cruz provinces) to better constrain the size of Arrokoth. The average spacing between these telescopes was around 4 km (2.5 mi). Using the latest observations from Hubble, the position of Arrokoth was known with much better precision than for the 3 June occultation, and this time the shadow of Arrokoth was successfully observed by at least five of the mobile telescopes. Combined with the SOFIA observations, this put constraints on possible debris near Arrokoth. Results from the occultation on 17 July showed that Arrokoth could have had a very oblong, irregular shape or be a close or contact binary. According to the duration of the observed chords, Arrokoth was shown to have two "lobes", with diameters of approximately 20 km (12 mi) and 18 km (11 mi), respectively. A preliminary analysis of all collected data suggested that Arrokoth was accompanied by an orbiting moonlet about 200–300 km (120–190 mi) away from the primary. It was later realized, however, that an error with the data processing software resulted in a shift in the apparent location of the target. After accounting for the bug, the short dip observed on 10 July was considered to be a detection of the primary body. By combining data about its light curve, spectra (e.g. color), and stellar occultation data, illustrations could rely on known data to create a concept of what it might look like prior to spacecraft flyby.
=== 2018 occultations ===
There were two potentially useful Arrokoth occultations predicted for 2018: one on 16 July and one on 4 August. Neither of these were as good as the three 2017 events. No attempts were made to observe the 16 July 2018 occultation, which took place over the South Atlantic and the Indian Ocean. For the 4 August 2018 event, two teams, consisting of about 50 researchers in total, went to locations in Senegal and Colombia. The event gathered media attention in Senegal, where it was used as an opportunity for science outreach. Despite some stations being affected by bad weather, the event was successfully observed, as reported by the New Horizons team. Initially, it was unclear whether a chord on the target had been recorded. On 6 September 2018, NASA confirmed that the star had indeed been seen to dip by at least one observer, providing important information about the size and shape of Arrokoth. Hubble observations were carried out on 4 August 2018, to support the occultation campaign. Hubble could not be placed in the narrow path of the occultation, but due to the favourable location of Hubble at the time of the event, the space telescope was able to probe the region down to 1,600 km (990 mi) from Arrokoth. This is much closer than the 20,000 km (12,000 mi) region that could be observed during the 17 July 2017 occultation. No brightness changes of the target star have been seen by Hubble, ruling out any optically thick rings or debris down to 1,600 km (990 mi) from Arrokoth. Results of the 2017 and 2018 occultation campaigns were presented at the 50th meeting of the American Astronomical Society Division for Planetary Sciences on 26 October 2018.
== Exploration ==