This month Unistellar citizen astronomers across North America will have the opportunity to detect a special type of asteroid with their eVscope!
On the morning of April 7, a Trojan asteroid known as 9142 Rhesus will occult (pass in front of) a star from our view here on Earth. It will be visible across a path sweeping over North America, through central Canada and the United States from North Dakota on down to Florida.
Rhesus was discovered in 1977 by the Dutch astronomer couple Ingrid and Cornelis van Houten, along with the Dutch–American astronomer Tom Gehrels. This trio is known for over several thousand asteroid discoveries.
What is a Trojan asteroid?
Trojan asteroids are located in two large groupings which orbit ahead and behind Jupiter. They were most likely captured 4 billion years ago during Jupiter’s migration towards the Sun, so they may contain clues on the history of our solar system.
Trojan asteroids are sometimes referred to as Jupiter trojans or just Trojans. 9,327 Trojan asteroids have been discovered as of February 16, 2021, though almost 2 million are estimated to exist.
Each Trojan is named from a figure of the Trojan War from Greek mythology.
9142 Rhesus gets its name from the Iliad, the ancient epic poem presumably written by Homer. Rhesus was king of Thrace and fought on the side of the Trojans.
The first Trojan asteroid was discovered in 1908 and was named 588 Achilles, after the legendary hero of the Trojan War and central character of the Iliad.
Rhesus is about 26 miles (42 kilometers) across, which makes it one of about an estimated 1 million Trojans that are larger than 0.6 mile (1 kilometer) across. In comparison, Achilles is about 83 miles (133 kilometers), making it one of the ten largest Trojan asteroids known.
NASA’s future exploration of Trojan asteroids
Trojan asteroids are a scientific priority for Unistellar because the first-ever mission to study them is underway. NASA’s Lucy spacecraft will launch in October 2021 and visit 5 different Trojans. Lucy will provide new insights into the primordial objects that formed the planets of our solar system, the origins of Earth, and even the formation of life.
The Unistellar team already successfully detected two of the Trojans that Lucy will visit. Read more about the Unistellar team’s positive detections of 21900 Orus and 11351 Leucus. Later this year, Unistellar citizen astronomers will even have the opportunity to detect the other three Trojans that Lucy will visit: 617 Patroclus, 3548 Eurybates, and 15094 Polymele!
This is a great opportunity for you to participate in this program and bring in new data for NASA.
Ready to observe?
Since no models of Rhesus’ shape exist currently, if you detect Rhesus, we may be able to generate its first shape model!
Check out our asteroid occultation predictions page for more details on this occultation including location, timing, and more.
- Click on North America on the drop-down menu and scroll down the page until you find 9142 Rhesus. Then, click on it.
- A map of North America with the path of the occultation should appear below.
- Zoom into the map so you can see the exact location where you can observe this occultation.
- Check the information above the map to make sure you have the correct parameters and observe for the correct duration.
If you have any questions, please reach out to us at firstname.lastname@example.org.