Near-Earth objects and close calls

SOMETHING JUST HIT JUPITER: Last night, Sept. 13-14, German astronomer Harald Paleske was watching the shadow of Io create a solar eclipse in the atmosphere of Jupiter when something unexpected happened. "A bright flash of light surprised me," he says. "It could only be an impact." Follow the arrows to the fireball:​

Paleske video-recorded the event. Reviewing the frames, he quickly ruled out objects such as airplanes and satellites, which might be crossing Jupiter at the time of his observation. The fireball was fixed in Jupiter's atmosphere. It first appeared at 22:39:27 UT on Sept. 13th and remained visible for a full two seconds.

The most likely explanation is a small asteroid or comet striking the giant planet; an asteroid in the 100m size range would do the trick.​

This isn't the first time astronomers have seen things hitting Jupiter. The most famous example is Comet Shoemaker-Levy 9 (SL9), which struck Jupiter in July 1994. At the time, most astronomers thought such collisions were rare, happening every hundred years or so. Since SL9, however, amateur astronomers using improved low-light cameras have observed more than a dozen impact flashes in Jupiter's cloudtops. The Solar System is more dangerous than we thought.

Paleske pinpoints the fireball at Jovian latitude 106.9° (CM1), longitude +3.8°. Other observers are encouraged to monitor the location for debris. Previous impacts have sometimes created inky clouds -- probably the remains of the impactor itself mixed with aerosols formed by shock-chemistry during the explosion.​

The event was also recorded in Brazil.

Brazilian observer José Luis Pereira captured a bright flash on the solar system's largest planet Monday night (Sept. 13), memorializing the fiery death of a space rock high in the Jovian atmosphere.

"I am an assiduous planetary observer," Pereira told in a written statement Tuesday (Sept. 14). "When the planets Jupiter, Saturn and Mars are in opposition, I try to make images in every possible night of clear skies. Especially [of] the planet Jupiter, my favorite."

On Sunday (Sept. 12) and Monday, Pereira set up his equipment in São Caetano do Sul, in the southeastern Brazilian state of São Paulo. As on many other nights, he aimed to photograph Jupiter and capture videos for the DeTeCt program, which seeks to spot and characterize impacts on the giant planet.

The weather didn't look like it would cooperate on Monday night, but Pereira persevered, collecting a series of 25 Jupiter videos, with no time gap between them.

"To my surprise, in the first video I noticed a different glow on the planet, but I didn't pay much attention to it as I thought it might be something related to the parameters adopted, and I continued watching normally," Pereira wrote. "So as not to stop the captures in progress for fear that weather conditions would worsen, I didn't check the first video."

He fed the videos into the DeTeCt program and then went to bed.

"I checked the result only on the morning of the 14th, when the program alerted me to the high probability of impact and verified that there was indeed a record in the first video of the night," Pereira wrote.

He then sent the information to Marc Delcroix of the French Astronomical Society, who confirmed that Pereira had indeed recorded footage of an impact that occurred Monday at 6:39 p.m. EDT (2239 GMT).

"For me it was a moment of great emotion, as I have been looking for a record of [such an] event for many years," Pereira wrote.

His observing setup consists of the following, he added: a Newtonian Telescope 275mm f/5,3 with a QHY5III462C camera, plus a Televue Powermate 5x (f/26,5) eyepiece and an IRUV cut filter. If you're looking to learn more about how to photograph planets, check out our astrophotography for beginners guide for the basics. You can also see how the Nikon Z6 camera stacks up for astrophotography here.

You can see more of Pereira's astronomical work on Flickr and YouTube.
How do you reliably avoid confusing incoming space junk with a fireball?
In the past, I have been wondering if some of the observed fireballs were actually incoming space junk colliding with the atmosphere.

The speed of a satellite in low orbits is around 16,000 miles/hour or /25,000km/hour or 7 km/s and rather slow for a meteoroid, since the Wiki claims speeds "typically in excess of 20 km/s"

When one studies the NASA Bolide data, the slowest of those that are calculated is just below 10 km/s (9.8 km/s), thus significantly higher than 7 km/s. But apart from burning up or meeting resistance from the atmosphere, some may still accelerate, so the 7 km/s may not be trustworthy either. This page Impact Cratering Mechanics, claims that the limit for an object from space is 11.2 km/s which is the escape velocity in the gravity field of the Earth, but does that hold for space junk too? How can one distinguish?
Meteor network cameras can be a little off, sometimes
I did a post about the 3600-year cluster in Session 3 August 1996 if anyone has interest. It came about after I read news of a meteor captured on the local network that indicated an initial speed of 74 km/s and an eccentricity of the orbit >2 meaning no orbit at all. After noticing an article from 2020: The challenge of identifying interstellar meteors. I asked the meteor group admin on FB about the high speed. He answered this morning that one camera had been installed in a temporary location and was a little off. It had now been corrected, and the data recalculated, leading to a less surprising speed, but still fast. The speed is now 64 km/s and the meteor has been estimated to belong to the September Epsilon Perseids.

The problems raised by the article on interstellar dust goes beyond this instance. Some meteor streams are very fast, and their orbits are very eccentric. While a camera may be good for recording the optical event, the computer program analyzing the data might give one more apparent accuracy than the physical set up can really justify. What helps a network is when there are several observations, then they between themselves can check who and what might be off. In this case there were three cameras, but for the speed only two. Sometimes there are four or five cameras on one meteor, and if the cameras are well-adjusted, that should give more reliable calculations.
@c.a. Regarding your post with the recent impact on Jupiter which included a Tweet:
Here's a much clearer look at the object that struck Jupiter on Monday, via Harald Paleske. It was probably a comet or asteroid about 100 meters in diameter -- small but potent.
Below are comments on why an object hits so hard when impacting Jupiter and what we may be able to learn from it.

This page, Impact Cratering Mechanics has considered the average impact velocities on other planets. First the image for the inner solar system where the Earth is located:
The impact velocities for Mercury, and to a less extent Venus are affected by the mass of the Sun while that of the Moon is affected by that of the Earth. On Earth the escape velocity is 11.1 km/s and the average impact velocity is around 18 km/s. Knowing these makes it easier to imagine what the situation on Jupiter is.

For the outer planets the average impact velocities are considered for the impact of dust particles, which are easier to work mathematically, with when knowing the escape velocities. Here one finds, that on Jupiter the escape velocity is 59.4 km/s, about 5 times the escape velocity on Earth or alternatively a little more than three times the average impact velocity on Earth.
03 (1).jpg
And the text below the images explains:
This illustration plots the log mass of the outer solar system planets against the minimum impact velocities of dust from Kuiper Belt objects for each body. Average impact velocities are still unknown. The impact velocities shown here are the escape velocities for the gas giants: 59.4 km/s for Jupiter, 35.4 km/s for Saturn, 21.2 km/s for Uranus, and 23.4 km/s for Neptune. Planetary mass is one factor that determines the velocity of objects impacting a planetary body. As the mass increases, so does the impact velocity. In the outer solar system, this holds true for all the gas giants. In comparison, Comet Shoemaker-Levy 9 impacted Jupiter at a velocity of 60 km/s. Impact velocities are plotted in kilometers per second on the lower x-axis and miles per second on the upper x-axis.

Illustration Credit: LPI (Andrew Shaner & David A. Kring). Background image of Saturn courtesy of NASA/JPL/Space Science Institute, PIA11613.

Source of Data: Moses, J. I. (2001) Meteoroid Ablation on the Outer Planets, Lunar and Planetary Science Conference XXXII, Abstract 1161.
If the object that recently impacted Jupiter had the same velocity as its own escape velocity, the same as Shoemaker-Levy, then it would have an impact energy that is approximately 10 times that of the average impact on Earth for the same physical properties in terms of mass and size.

According to Impact Cratering Mechanic 53 km/s is the average speed of long-period comets with a period of 200-1000 years. If we make a guess that near-hyperbolic comets with periods of more than a 1000 do not have much less velocity on average, then impacts of a comet from the Oort cloud could impact the Earth with close to as much power as the recent hit on Jupiter, if it had the same physical properties. Isn't that sobering?
How do you reliably avoid confusing incoming space junk with a fireball?
In the past, I have been wondering if some of the observed fireballs were actually incoming space junk colliding with the atmosphere.
When the discussed rainfall of satellites starts, we'll have ample material to compare regular meteorite impacts and burnt satellite metal junk remaining intact enough to smash house roofs.
This morning, I was able to catch the lunar collision flash for the first time in a long time! This is a telescope shot of the lunar collision flash that occurred at 4:33:10 on October 3, 2021 from my home in Hiratsuka. Since there is no atmosphere on the moon, craters are generated instead of becoming meteors, and the light that shines at that moment is called the lunar collision flash.
This was taken with another telescope at the same time. Since there were no satellites in the catalog that glowed over multiple frames and passed through the lunar surface, there is a high possibility of a lunar collision flash

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