Science

A giant comet flies straight towards the sun, but does not fall apart

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While comet hunters look at the “green” comet ZTF 2022 E3, SOHO and NASA instruments point to Comet 96P Machholtz moving in the opposite direction, directly towards the Sun. It reached perihelion (the closest point to the Sun) on January 31, 2023. Unlike other comets that were destroyed too close to the Sun, this city-sized comet (6 kilometers) survived. The astronomer suggests that it may have an extrasolar origin.

96P, or Machholz 1, named after amateur astronomer Don Machholz who discovered it in 1986, is a medium-sized comet with a relatively short period and a low orbital inclination controlled by Jupiter’s gravitational influence. It revolves around the Sun every 1930 days.

NASA’s Jet Propulsion Laboratory has classified 96P/Machholz 1 as a “near-Earth asteroid” due to its close orbit to Earth, but it is not considered potentially dangerous as computer simulations did not indicate an imminent impact.

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Unlike many solar-directed comets less than 10 meters in diameter, which therefore burn up, Machholtz 1 appears to be protected from complete evaporation by its size. According to recent estimates, its diameter is more than two-thirds of the height of Mount Everest, or more than 6 km.

It is also thought to be the source of the Arietids, an intense meteor shower that is active from May 22 to July 2 of each year.

Recently, as Comet c/2022 E3 (ZTF) appears in the northern night sky, Comet 96P Machholz 1 appears from the opposite direction and completes its orbit between the Sun and Earth. It reached perihelion (the closest point to the Sun) on January 31, 2023. At the same time, the comet reached perigee (the closest point to Earth).

extrasolar comet

Comet Machholtz 1 is not like the others. Carl Battams, who leads the Sungrazer project at the US Naval Research Laboratory, tweeted Jan. 29: “96P is one of the strangest comets in the solar system in terms of composition and behaviour.”

These LASCO SOHO images show the comet approaching and reaching its orbital turn point, and changes in the comet’s tail due to the solar wind can be seen as it reaches perihelion and begins its orbital revolution. © NASA/SOHO LASCO

What’s more, David Schleicher of the Lowell Observatory in Flagstaff, Arizona, studies the chemistry of comets. He found, after analyzing 150 of them, that they all had the same levels of the chemical cyanogen (CN), with the exception of Machholz 1, which has less than 1.5% of normal levels. Like some other comets, it is low in C2 and C3 molecules. Schleicher offers three possible explanations.

First, the simplest is that Machholz 1 could have formed in an extremely cold region of the solar system, outside of the Kuiper belt and far beyond Neptune, being depleted in carbon molecules. This is because low temperatures mean that most of the carbon is trapped in other molecules.

Secondly, this comet visits the Sun several times, so it is possible that these repeated encounters with the heat emitted by the Sun removed most of its cyanogen.

Finally, it could be that Machholz 1 is of extrasolar origin. In the NewScientist article, the researcher explains: “An extrasolar origin makes it easier to explain the composition — of course, we would expect things to be different. Here, all three carbon-containing molecules are depleted, so maybe carbon is depleted at all levels? As if the comet came from somewhere else and wasn’t just a feature of our solar system.”

The comet may have found itself in its strange, highly eccentric orbit after being ejected from its home star system by the giant planet’s gravity. Then, after a significant time wandering through space, an accidental collision with Jupiter could change its trajectory to trap it around our star. Its orbit, the smallest perihelion distance known among short-period comets, brings it much closer to the Sun than Mercury’s orbit.

SOHO comet watcher

The Solar and Heliospheric Observatory SOHO (a joint mission of the European Space Agency and NASA) was not intended to search for comets – its original purpose was to study the Sun from its deep core to the outer layers beyond its atmosphere.

But almost 25 years after its launch, data from this space-based solar observatory has led to the discovery of more than half of all known comets, or more than 4,500 new comets discovered in July 2022, according to the Sungrazer website. Research laboratory. It is a NASA-funded project managed by Battams, born out of the first discoveries of civilian comets shortly after the launch of SOHO in 1995.

Carl Battams explains in a press release: “SOHO is uniquely located in space and has a unique design, and it is these characteristics that allow it to observe and discover so many comets.”

Indeed, SOHO is equipped with a coronagraph equipped with a solid disk that blocks the central light coming from the Sun, exposing the outer atmosphere (much less luminous), the corona. Scientists use these images of the corona to study how this part of the atmosphere is changing and to track random bursts of material from the Sun called coronal mass ejections. SOHO’s viewpoint between the Sun and Earth, about a million miles away, gives it a constant view of the solar atmosphere.

Known as LASCO, the SOHO coronagraph has high sensitivity and a wide field of view, making it ideal for detecting “solar comets” that pass too close to the Sun to be seen from Earth or most other scientific instruments.

Comets detected by SOHO act as “celestial windsocks,” revealing new information about the wind and solar atmosphere they pass through, according to NASA.

VIDEO: slow-motion footage of the comet’s passage (© Ron Murphy)

As comets approach the Sun, they are covered in a tail of gas given off by the comet as it heats up from the intense radiation. Some of the gases in this tail are ionized and exposed to the magnetized solar wind and the magnetic fields of the outer atmosphere, giving scientists the ability to measure conditions in this region that would otherwise be invisible, as we can clearly see in the previously presented photographs of Comet Machholz 1. ” We used these images to test models of the solar magnetic field and various elements such as electron density and temperature,” says Battams.

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