Astronomers Measure The Asteroid Between Mars and Jupiter

  • Palma asteroid revolves around the Sun and completes one revolution in 5.59 years.
  • In May 2017, Palma eclipsed the radio waves coming from radio galaxy.
  • Astronomers analyzed these signals and measured characteristics of Palma. 

In a strange observation, researchers studied radio waves coming from a far-away radio galaxy when an asteroid in our Solar System came in front of this radio galaxy. Using Very Long Baseline Array (VLBA) — a system of 10 radio telescopes — they precisely measured the asteroid’s size, shape and orbital path.

The galaxy continuously emits radio waves towards Earth but when an asteroid comes in the front of this galaxy, the waves get slightly diffracted (bent around the edge of the asteroid). As these waves interact with each other, they create weaker and stronger waves with circular shapes. The same happened in this observation.

Researchers at the University of Helsinki in Finland analyzed the diffracted radio waves’ patterns to get more insight of the asteroid, including its location, size, and shape. The result and conclusion are based on readings captured on 15th May 2017 using 6 antennas of VLBA.

New Observations Are 10 Times Better

The asteroid they have studied is called Palma. It’s in the main asteroid belt between Mars and Jupiter discovered in 1893. It revolves around the Sun and completes one revolution in 5.59 years.

On 15th May 2017, Palma eclipsed the radio waves coming from 0141+268 galaxy. When radio shadow reached Earth’s surface (at the speed of over 51 km/s), it was first detected by VLBA station in Washington.

Reference: arXiv:1804.05640 | NRAO

The parameters of radio signals change whenever an asteroid passes in the front of the radio galaxy (the event is referred as occultation). The modern instruments used in VLBA are capable enough to detect this change and help researchers deduce the nature of the asteroid.

After all necessary measurements and analysis, they found that Palma has 192 km of diameter. Like other asteroids, it’s not perfectly round in shape: it has an irregular structure with one edge hollowed out.

Usually, astronomers observe these types of signals and capture the alteration in asteroid’s intensity or brightness as it passes in front of stars or radio galaxies. This VLBA observation is quite special because it enabled them to calculate the phase shit (wave peaks displaced by the diffraction).

The possibility of calculating both the phase and amplitude of the diffraction wavefront significantly raise the accuracy of the asteroid sizing as compared to single-dish data. The maximum phase shift is especially sensitive to the asteroid’s diameter. It puts a constraint on the structure of the asteroid with a single, short measurement.

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Although locations of Palma have been calculated over 1,600 times over the past 12 decades, this measurement improved the certainty in the estimated orbit by a factor of 10. In the next study, researchers will combine the current radio signal with previous optical observations to precisely determine the shape of the asteroid.

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