2017 YE5
Binary near-Earth asteroid likely originating as an extinct comet.
2017 YE5 is a binary asteroid system made up of two roughly equal-sized bodies, each around 0.9 kilometers across. It is classified as a near-Earth object and a potentially hazardous asteroid belonging to the Apollo group. French amateur astronomer Claudine Rinner discovered it on December 21, 2017, using the Oukaïmeden Observatory in Morocco. The discovery was part of the Morocco Oukaïmeden Sky Survey (MOSS), led by Zouhair Benkhaldoun at Cadi Ayyad University. The survey aimed to find and track small Solar System bodies like near-Earth asteroids and comets. 2017 YE5 was the sixth near-Earth asteroid found by MOSS, spotted in images from the observatory’s 0.5-meter reflecting telescope, which Rinner operated remotely. At the time, it was about 1.1 astronomical units (160 million kilometers) from Earth, in the constellation Gemini, with an apparent magnitude of 19.8.
The discovery was reported to the Minor Planet Center’s Near-Earth Object Confirmation Page, where a preliminary orbit was calculated using additional observations from several observatories. Follow-up observations over six days after discovery led to its formal announcement in a Minor Planet Electronic Circular on December 27, 2017. Precovery observations were later identified: the Mount Lemmon Survey had spotted it on December 14, 2017, a week before discovery, and the Pan-STARRS1 survey had observed it on December 12, 2017—the earliest known sighting—reported in May 2018.
Initially given the internal designation tltv005, the object received the provisional designation 2017 YE5 on December 27, 2017. This code indicates it was the 130th object discovered in the second half of December 2017. It has not yet received a permanent minor planet number because its observation arc of 270 days is too short for a precise orbit. It will likely get a number after being observed over at least four oppositions, which will take several years, and then it will become eligible for naming.
2017 YE5 orbits the Sun at an average distance of about 2.82 astronomical units, completing one orbit every 4.73 years. Its orbit is slightly inclined to the ecliptic by 6.2 degrees, with its farthest point below the ecliptic. The orbit is highly elongated, with an eccentricity of 0.71: at perihelion it comes within 0.82 AU of the Sun, and at aphelion it reaches 4.82 AU, beyond the outer asteroid belt.
- Discovery date
- 21 December 2017
- Discoverer
- Claudine Rinner
- Discovery site
- Oukaïmeden Observatory, Marrakesh, Morocco
- Diameter
- each about 0.9 km (0.56 mi)
- Closest earth approach
- 15.5 lunar distances (approx. 6 million km) on 21 June 2018
- Orbital period
- 4.73 years
- Earth moid
- 0.021 AU (3.1 million km)
Lore & Background
2017 YE5 was discovered on 21 December 2017 by French amateur astronomer Claudine Rinner at the Oukaïmeden Observatory in Morocco, as part of the Morocco Oukaïmeden Sky Survey (MOSS) directed by Zouhair Benkhaldoun. At discovery, it was about 1.1 AU from Earth in the constellation Gemini at magnitude 19.8. Precovery observations were later identified from the Mount Lemmon Survey (14 December 2017) and Pan-STARRS1 (12 December 2017).
The asteroid orbits the Sun with a semi-major axis of 2.82 AU, high eccentricity of 0.71, and inclination of 6.2 degrees. Its Tisserand parameter of 2.877 is characteristic of comets, and its dark red surface and low albedo support classification as an extinct or dormant Jupiter-family comet. It is classified as an Apollo group near-Earth object and potentially hazardous asteroid, though it poses no impact risk for at least 200 years.
During its close approach on 21 June 2018, the binary nature was revealed by radar observations at Goldstone, Arecibo, and Green Bank observatories. The two components are roughly equal in size, and optical observations later detected possible mutual eclipses between them.
Reader's Guide
The significance of 2017 YE5 lies in its binary nature and its likely cometary origin, both of which were clarified during its close Earth encounter in June 2018. Radar observations by Goldstone, Arecibo, and Green Bank resolved the two components at high resolution, confirming them as a binary pair of nearly equal size. This made 2017 YE5 one of the few known equal-mass binary near-Earth asteroids.
Its comet-like Tisserand parameter and dark red surface suggest it is an extinct or dormant Jupiter-family comet, providing a rare opportunity to study a transition object between cometary and asteroidal states. The discovery by an amateur astronomer as part of the MOSS survey highlights the role of small surveys in detecting potentially hazardous objects.
Although classified as a potentially hazardous asteroid, its orbit is well-characterized, and it poses no threat for the next two centuries. The 2018 encounter allowed detailed radar and optical observations that will inform future studies of binary systems and cometary evolution.
Did You Know?
- It is a binary pair with each component about 0.9 km in diameter.
- The asteroid passed within 15.5 lunar distances of Earth on 21 June 2018.
- Its dark red surface and comet-like Tisserand parameter suggest it is an extinct or dormant comet.
Frequently Asked Questions
What is 2017 YE5?
It is a binary near-Earth asteroid in the Apollo group, composed of two nearly identical bodies that orbit one another. Because its path brings it into the neighborhood of Earth's orbit, it is flagged as a potentially hazardous object.
Who discovered 2017 YE5 and where?
French amateur astronomer Claudine Rinner first detected it on 21 December 2017 using the Oukaïmeden Observatory near Marrakesh, Morocco. The observation was made under the Morocco Oukaïmeden Sky Survey, a program led by Zouhair Benkhaldoun at Cadi Ayyad University to catalogue small Solar System bodies.
How big is 2017 YE5?
Each of the two component bodies in the binary pair measures roughly 0.9 kilometres (about 0.56 miles) across, making them almost the same size. That gives the system a notably compact, twin-like appearance compared with many other near-Earth asteroids.
How close did 2017 YE5 come to Earth?
Its nearest recorded fly-by happened on 21 June 2018, at a distance of about 15.5 lunar distances, or roughly 6 million kilometres. That is well beyond the Moon's orbit, so the pass posed no real danger to the planet.
Why do asteroid fans find 2017 YE5 interesting?
Beyond its neat binary structure, many researchers believe it is actually the rocky remnant of an extinct comet that shed its ice over billions of years. Its 4.73-year orbital period and Apollo-group classification make it a valuable case study for understanding how cometary nuclei behave once they migrate into the inner Solar System.
More in Notable Asteroids 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced