In June 2019, the ATLAS (Asteroid Terrestrial-impact Last Alert System) automatic survey found a new object moving on the background stars. Originally named 2019 LD2, it was thought to be an asteroid orbiting the Sun near Jupiter. However, an amateur astronomer noticed that it appeared to be unclear, not resembling a dot, which means it looks more like a comet: The frozen material on the surface turns into a gas as it is heated by the Sun.
Checking the archived images, astronomers determined that it was “active” for at least a few months. The object’s name was then changed to P / 2019 LD2, indicating its status as a periodic comet.
Images from other observers have confirmed this, including Hubble. When they looked at the comet in April 2020, they saw it carrying a rather large tail, extending about 600,000 kilometers, almost twice the distance of the moon from Earth! Beware, the nucleus – the solid part of the comet – is probably only 4 kilometers long.
Calculations show that at that time he was losing about 80 kilograms of ice water per second. It also releases gases such as carbon monoxide (about 50 kilograms / second), carbon dioxide (7 kilograms / second) and diatomaceous earth (two carbon atoms bound together; at a rate of 40 grams per second).
It may sound like a lot, but it seems just it started to devalue like that … and it won’t last long. Its status as a periodic comet is only temporary. Extremely temporarily: tracking measurements to determine its orbit have found that it is in fact in an orbit similar to that of Jupiter and there is an excellent chance that, in the distant future, the strong gravity of the giant planet will launch the comet from the solar system.
When this happens, it will become an interstellar comet like 2I / Borisov or ‘Oumuamua, interstellar objects that have recently passed through our solar system (and which, I will note, are not alien spaceships).
This is appropriate, because life probably started outside the solar system as well.
Probably P / 2019 LD2 started as what is called a Trans-Neptunian object, an ice body orbiting the Sun in the Kuiper Belt outside Neptune. Over time, very gentle blows of Neptune’s gravity prompted him into a smaller orbit closer to the Sun. Eventually, it came close enough that Neptune could pull it out much harder, substantially changing its orbit, placing it in an orbit between that of Jupiter and Neptune (from about 800 million to 3 billion kilometers from the Sun). Objects in such orbits are named Centaurs.
Centaurs are interesting. Over time, gas giants tend to change their orbits even more. In general, after several million years in this part of the solar system, they are getting too close to one of the planets. Either they are thrown into the inner solar system (and become what we call the comets of the Jupiter family), or they are thrown out of the entire solar system. That’s why we call them transition objects*.
What will be the fate of P / 2019 LD2? And where did it originally come from?
Time observations of an object can be used to determine its orbit, which can then be projected into the past and future. The problem is that we can’t measure the orbit exactly; there is always a certain uncertainty in it. The more you try to predict its position in the future (or predict your position in the past), the more fuzzy it becomes, the larger the amount of space it could take up. This makes this type of prognosis difficult.
To avoid this, astronomers did something clever: they simulated its orbit using what is called a Monte Carlo technique. They take the physical characteristics of the orbit (shape, distance from the Sun, tilt and so on) and then change each one very easily, creating a slightly different orbit. Then they move on to the past and the future and see what he does. They do this over and over again, creating a virtual cohort of objects, each with marginally different paths. In this way, you will get a more statistical idea of what was and will be the history and future of the object.
What they found for P / 2019 LD2 is that it probably entered Jupiter’s space only about 2.5 years ago! Before that, it was a Centaur with standard problems, but it was recently introduced into its current orbit.
And his future? They probably found that it would only remain in its current orbit Another 8 or 9 years. After that, it will probably fall into the inner solar system, becoming a comet of the Jupiter family. This means that it only makes a stop in the pit near Jupiter.
Even this is temporary. It has a 50% decrease in the solar system in 340,000 years, which rises to 95% in 4 million years.
Probably billions of such objects have been removed over the age of the solar system. And there are billions of stars like the Sun … which is why astronomers believe that the galaxy is loaded with dishonest interstellar ice balls like P / 2019 LD2 and why it’s not so surprising that we see them passing through our solar system.
Will some alien scientists see LD2 going through their own system in the distant future? What would he make of it? It is funny and strangely reassuring to know that pieces of our neighborhood will be scattered among the stars, ranging from citizens of our solar system to citizens of the galaxy.
*Which is pretty cool, it worked this way, given that they are named after mythical creatures half man / half horse.