• Post category:Space Probes
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In our previous article, we discussed the second phase of the New Horizons’ space probe i.e. journey to Pluto. Today we will move on to the third phase i.e. close fly-by of 486958 Arrokoth (Fig 1). It is a trans-Neptunian object located in the Kuiper belt. Arrokoth is a contact binary 36 km (22 mi) long, composed of two planetesimals 21 km (13 mi) and 15 km (9 mi) across, nicknamed “Ultima” and “Thule”, respectively, that are joined along their major axes (Fig 2).

Fig 1. Color composite image of Arrokoth
Fig 1. Color composite image of Arrokoth
Fig 2. Illustration depicting the formation sequence of Arrokoth.
Fig 2. Illustration depicting the formation sequence of Arrokoth.

Encounter with Arrokoth

Having completed its flyby of Pluto in July 2015, the New Horizons spacecraft placed itself on a trajectory towards Arrokoth. It is the first object to be targeted for a flyby that was discovered after the visiting spacecraft was launched, and is the farthest object in the Solar System ever to be visited by a spacecraft. New Horizons passed by Arrokoth at a distance of 3,538 km with the closest approach occurring on 1st January 2019. At that distance, the one-way transit time for radio signals between Earth and New Horizons was 6 hours.

Objectives of the fly-by

  • Characterizing the geology and morphology of Arrokoth
  • Mapping the surface composition (by searching for ammonia, carbon monoxide, methane, and water ice)
  • Searching for any signs of activity, such as a cloud-like coma
  • Searching for, and studying, any satellites or rings

The object has no detectable atmosphere, and no large rings or satellites larger than 1.6 km (1 mi) in diameter. Nonetheless, a search for a related moon (or moons) continues, which may help better explain the formation of Arrokoth from two individual orbiting objects.

Data download

After the encounter, preliminary, high-priority data was sent to Earth on January 1 and 2, 2019. On January 9, New Horizons returned to a spin-stabilized mode, to prepare to send the remainder of its data back to Earth. This download is expected to take 20 months at a data rate of 1–2 kilobits per second. The download of data is expected to be completed in September 2020, thereafter new insights about Arrokoth will be revealed.
With this, we come to the end of the New Horizons series. Next time we will come with a new topic for discussion.


  1. https://en.wikipedia.org/wiki/New_Horizons
  2. https://www.nasa.gov/mission_pages/newhorizons/main/index.html
  3. https://en.wikipedia.org/wiki/Tvashtar_Paterae
  4. http://pluto.jhuapl.edu/
  5. http://pluto.jhuapl.edu/Mission/The-New-Horizons-Mission.php
  6. https://www.space.com/new-horizons-arrokoth-ultima-thule-flyby-one-year-later.html
  7. https://en.wikipedia.org/wiki/486958_Arrokoth#Exploration

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