The asteroid that past very close the Earth turned out to be more compact than expected

(Luisa Fernanda Zambrano-Marin et al. / The Planetary Science Journal, 2022 https://bit.ly/3OxACi1)

The asteroid 2019 OK turned out to be a strong rapidly rotating body with a diameter of 70 to 130 meters.

The near-Earth asteroid was discovered a day before the closest approach to the Earth in 2019.

2019 OK was discovered on July 24, 2019 by the SONEAR (Southern Observatory for Near-Earth Asteroids Research) observatory.

A day later, the asteroid approached our planet at a minimum distance of 11.2 Earth radii (around 72,000 kms), while moving at a speed of 24.53 km/s.

This space rock belongs to the Apollo group, and its orbit is characterized by a large eccentricity and an orbital period of 2.55 years.

The next approach 2019 OK with the Earth will occur on July 28, 2093, and the minimum distance between objects will be 0.053 AUs (around 8 million kms).

However, the exact details of the asteroid were difficult to pinpoint due to small bodies located near the opposition point.

Now, a team of astronomers from the Arecibo Observatory in Puerto Rico published the results of radar observations of the asteroid 2019 OK.

The team, led by Luisa Zambrano-Marin used the, now collapsed, Arecibo 300-meter radio telescope at a frequency of 2380 megahertz on July 25, 2019.

The observations began 41 hours after the discovery of the asteroid and lasted just under 3 hours, until the asteroid reached a distance of 3.8 Earth-Moon distances.

The team also analyzed optical observations from 9 ground-based observatories of 2019 OK from February 21, 2017 to July 25, 2019.

The asteroid’s determined apparent diameter ranged from 70 to 130 meters. This, combined with the absolute magnitude H=23.3, gives an optical albedo value of 0.05 to 0.17.

The period of rotation of the body around its axis is from 3 to 5 minutes: the asteroid was rotating very fast.

The asteroid cannot be classified as V- or E-type, instead it is classified as C- or perhaps as S-type.

The S-type bodies have a density of approximately 2.8 to 3.5 grams per cubic centimeter.

All of this means that 2019 OK cannot be classified as a "pile of rubble " like the asteroids Bennu or Ryugu, that are bound only by gravity.

The minimum cohesive strength required for an asteroid not to deform due to rotational speed is estimated to be at least 350 Pascals

However, the actual strength of 2019 OK’s material could be much greater: the rock was very compact.

Sources:

• The Planetary Science Journal: https://iopscience.iop.org/article/10.3847/PSJ/ac63cd
• Science Daily: https://www.sciencedaily.com/releases/2022/06/220623184239.htm

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