Inbound: Astronomers discover third interstellar object

Gaby Clark
scientific editor

Andrew Zinin
lead editor

Astronomy news always seems to break over coffee, on laptop startup. That was the case on Wednesday morning, when word of a curious new object started flashing across the message boards.
The object in question is currently at +18th magnitude, moving slowly along the border of the constellations Serpens Cauda and Sagittarius, right near the galactic plane. The object was captured on July 2nd by the Deep Random Survey remote telescope in Chile. The Asteroid Terrestrial-impact Last Alert System (ATLAS) based in Rio Hurtado made the discovery on July 1st. Sam Deen soon backed this up with pre-discovery images from worldwide ATLAS sites in Chile, Hawaii and South Africa from June 25–29.
This allowed astronomers to plot a preliminary orbit. That's where things get really interesting: the object has an eccentricity now estimated near 6.0—the highest seen yet. An eccentricity of 1.0 or lower is a closed orbit, signifying an asteroid or comet on an elliptical orbit in our solar system. This one is coming from interstellar space on a high inclination 175 degree orbit, perhaps originating from the .
David Rankin of the University of Arizona's Catalina Sky Survey notes on Blue Sky that this high eccentricity cinches the hyperbolic orbit of the object.
Right now, the object isn't showing any signs of cometary activity. Estimates by Marshall Eubanks (Asteroid Initiatives) suggests it may be an asteroid about 20 kilometers in size.
The object has a preliminary designation on the (NEOCP) as A11pl3Z. There should be a formal name within a day or so, and the object will receive an "I' designation for interstellar.
"It (A11pl3Z) is moving very fast, with a velocity about 60 kilometers per second. It may be considerably larger," Eubanks told Universe Today. "1I seems to be a young object, as it was moving near the local galactic 'standard of rest... by the same token, 3I is probably much older, probably comparable in age to the solar system."
The European Space Agency confirmed the discovery on Blue Sky:
The tale of Oumuamua and Borisov sets the precedent for the discovery. I1/2017 U1 ʻOumuamua was the first interstellar object discovered in 2017. That one was discovered on its outbound leg out of the solar system, sending astronomers scrambling to make observations before it faded from sight. Oumuamua also generated a fair amount of controversy, due to its inferred pancake shape, and its approach from what's known as the galactic 'local standard of rest," the reference frame that defines the motion of local stars around the galactic center. A fast mover, I1/Oumuamua was moving much too fast to chase down, although proposals were made.
The discovery of 2019 2I/2019 Q4 Borisov added to our small inventory of known interstellar objects.

A11pl3Z could prove different. First, it's still inbound, currently just inside the orbit of Jupiter. The object reaches perihelion in a few months on October 29th, 2025 at about 1.35 astronomical units (AUs) from the sun, exterior to the orbit of Mars. Intriguingly, A11pl3Z passes just 0.2 AU from Mars on October 3rd, and assets including the Mars Reconnaissance Orbiter may be able to nab it as an +11th magnitude object.
Unfortunately, Earth will be on the opposite side of the sun versus the object at perihelion. Closest Earth approach for the object occurs on October 30th, 2025, at 1.35 AU. Moving at 61 miles per second outbound, A11pl3Z will be moving much too fast for spacecraft to chase down.
But more crucially, we now have the James Webb Space Telescope and the recently commissioned Vera C. Rubin Observatory on hand to bring to bear on A11pl3Z. Vera C. Rubin discovered an on its very first time out.
Clearly, interstellar asteroids and comets are more common than were previously thought… we were simply missing most of them as they whiz through the solar system. We'll provide updates as the situation unfolds, and more is known about the enigmatic object A11pl3Z.
Provided by Universe Today