A new minimoon is headed towards Earth, and it’s not natural

Astronomers spot an object heading into Earth orbit.

A new minimoon is headed towards Earth, and it’s not natural
Credit: Tony Dunn
  • Small objects such as asteroids get trapped for a time in Earth orbit, becoming "minimoons."
  • Minimoons are typically asteroids, but this one is something else.
  • The new minimoon may be part of an old rocket from the 1960s.

    • From time to time, asteroids whizzing past Earth get trapped by our gravitational pull, falling into orbit around the planet. These rocks only stay for a while, eventually escaping and continuing on their journey to who-knows-where. While they're here, they're considered "minimoons."

      Astronomers have detected an object that's likely to become our next minimoon. But it's either not an asteroid or it's an odd one. Really, scientists suspect it's man-made tech returning home after many years out in cold, lonely space.

      Minimoons

      Scientists have confirmed just two prior minimoons. One was 2006 RH120, which orbited us from September 2006 to June 2007. The other was 2020 CD3, which got stuck in the 2015–2016 timeframe, and is believed to gotten away in May 2020.

      2020 SO, the new kid on the block, is expected to arrive in October 2020 and pop out of orbit in May 2021.

      Identifying 2020 SO

      The first clue 2020 SO isn't your ordinary asteroid is its exceptionally low velocity. It's traveling much more slowly that a typical asteroid — their average rate of travel is 18 kilometers (58,000 feet) per second. Even moon rocks sent careening into Earth orbit by impacts on the lunar surface outpace pokey 2020 SO.

      For another thing, 2020 SO has an orbital path very similar to Earth's, lasting about one Earth year. It's also just slightly less circular than our own orbit, from which it's barely tilted off-axis.

      So, what is it? NASA estimates that the object has dimensions very reminiscent of a discarded Centaur rocket stage from the Surveyor 2 mission that landed an unmanned craft on the moon. Back in the day, rocket stages were jettisoned as craft were aimed toward their desired position. This stuff, if released high enough, remains in space. It appears that this Centaur rocket, launched in September 1966, is now making its way back homeward, at least for a little bit.

      When 2020 SO arrives at its closest point in December, the rocket is expected to be about 50,000 kilometers from Earth. Its next closest approach is much further: 220,000 kilometers, in February 2021.

      Centaur rocket stage

      Centaur rocket stage

      Credit: NASA/Wikimedia

      What we may be able to learn

      Earthly space programs being as young as they are, scientists would love to know what's happened to our rocket during a half century in space.

      While 2020 SO won't get close enough to drop into our atmosphere, its slow progress has scientists hopeful that they'll still get some kind of a decent look at it.

      Spectroscopy may be able to reveal what the rocket's surface is like now — has any of its paint survived, for example? Of course, being out in space, it's likely to have been hit by lots of dust and micrometeorites, so the current state of its surfaces is also of interest. Experts are curious to know how reflective the rocket is at this point, valuable information that can help planners of future long-term missions anticipate how well a craft out in space for extended periods will remain able to reflect sunlight.

      This is what aliens would 'hear' if they flew by Earth

      A Mercury-bound spacecraft's noisy flyby of our home planet.

      Image source: sdecoret on Shutterstock/ESA/Big Think
      Surprising Science
      • There is no sound in space, but if there was, this is what it might sound like passing by Earth.
      • A spacecraft bound for Mercury recorded data while swinging around our planet, and that data was converted into sound.
      • Yes, in space no one can hear you scream, but this is still some chill stuff.

      First off, let's be clear what we mean by "hear" here. (Here, here!)

      Sound, as we know it, requires air. What our ears capture is actually oscillating waves of fluctuating air pressure. Cilia, fibers in our ears, respond to these fluctuations by firing off corresponding clusters of tones at different pitches to our brains. This is what we perceive as sound.

      All of which is to say, sound requires air, and space is notoriously void of that. So, in terms of human-perceivable sound, it's silent out there. Nonetheless, there can be cyclical events in space — such as oscillating values in streams of captured data — that can be mapped to pitches, and thus made audible.

      BepiColombo

      Image source: European Space Agency

      The European Space Agency's BepiColombo spacecraft took off from Kourou, French Guyana on October 20, 2019, on its way to Mercury. To reduce its speed for the proper trajectory to Mercury, BepiColombo executed a "gravity-assist flyby," slinging itself around the Earth before leaving home. Over the course of its 34-minute flyby, its two data recorders captured five data sets that Italy's National Institute for Astrophysics (INAF) enhanced and converted into sound waves.

      Into and out of Earth's shadow

      In April, BepiColombo began its closest approach to Earth, ranging from 256,393 kilometers (159,315 miles) to 129,488 kilometers (80,460 miles) away. The audio above starts as BepiColombo begins to sneak into the Earth's shadow facing away from the sun.

      The data was captured by BepiColombo's Italian Spring Accelerometer (ISA) instrument. Says Carmelo Magnafico of the ISA team, "When the spacecraft enters the shadow and the force of the Sun disappears, we can hear a slight vibration. The solar panels, previously flexed by the Sun, then find a new balance. Upon exiting the shadow, we can hear the effect again."

      In addition to making for some cool sounds, the phenomenon allowed the ISA team to confirm just how sensitive their instrument is. "This is an extraordinary situation," says Carmelo. "Since we started the cruise, we have only been in direct sunshine, so we did not have the possibility to check effectively whether our instrument is measuring the variations of the force of the sunlight."

      When the craft arrives at Mercury, the ISA will be tasked with studying the planets gravity.

      Magentosphere melody

      The second clip is derived from data captured by BepiColombo's MPO-MAG magnetometer, AKA MERMAG, as the craft traveled through Earth's magnetosphere, the area surrounding the planet that's determined by the its magnetic field.

      BepiColombo eventually entered the hellish mangentosheath, the region battered by cosmic plasma from the sun before the craft passed into the relatively peaceful magentopause that marks the transition between the magnetosphere and Earth's own magnetic field.

      MERMAG will map Mercury's magnetosphere, as well as the magnetic state of the planet's interior. As a secondary objective, it will assess the interaction of the solar wind, Mercury's magnetic field, and the planet, analyzing the dynamics of the magnetosphere and its interaction with Mercury.

      Recording session over, BepiColombo is now slipping through space silently with its arrival at Mercury planned for 2025.

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