Hubble detects small moon orbiting dwarf planet Makemake
Dwarf planet Makemake, the second brightest object in the Kuiper Belt, is orbited by a small, dark moon. The satellite was discovered by a team of scientists using the Hubble Space Telescope’s Wide Field Camera 3 (WFC3) from observations conducted in April 2015.
Because WFC3 has extremely sharp resolution, along with the capability of finding faint objects next to bright ones, this latest search, unlike several previous efforts, successfully detected the satellite.
The faint moon, designated S/2015 1 and nicknamed MK 2, is approximately 1,300 times fainter than Makemake itself. Orbiting at a distance of approximately 13,000 miles (21,000 kilometers) from its parent planet, MK 2 has an estimated diameter of 100 miles (160 kilometers), while Makemake’s diameter is about 870 miles (1,400 kilometers).
Led by Marc Buie of the Southwest Research Institute, the discovery team used the same technique and camera to discover Pluto’s four small moons in 2005, 2011, and 2012.
MK 2 is visible in the Hubble image as a faint dot just above Makemake.
Its discovery suggests that many dwarf planets in the Kuiper Belt, now viewed by some as the Solar System’s “third zone”, may also have satellites.
“Our preliminary estimates show that the moon’s orbit seems to be edge-on, and that means that often, when you look at the system, you are going to miss the moon because it gets lost in the bright glare of Makemake,” said Alex Parker, leader of the image analysis team at Southwest Research Institute.
By measuring the orbit of a satellite, scientists can study its parent body in far more detail than they could if that body orbited alone. Knowing a moon’s orbit makes it possible for scientists to accurately determine the planet’s mass, density, composition, and even origin.
Both Pluto and Makemake are covered in frozen methane. The calculation of Makemake’s density, mass, and composition could indicate the two objects have much in common.
“The discovery of this moon has given us an opportunity to study Makemake in far greater detail than we ever would have been able to without the companion,” Parker said.
Early studies show MK 2’s orbit around Makemake takes about 12 days to complete and is believed to be circular, suggesting it was formed by a collision between Makemake and another Kuiper Belt Object.
Moons in elliptical, elongated orbits are usually captured by their parent planet rather than formed via a collision.
Whether a collision or a capture, the event that created MK 2 would have happened in the early days of the Solar System, billions of years ago. Scientists will need to conduct more Hubble observations to confirm the moon’s orbit.
Finding MK 2 may also answer a question that has puzzled scientists since Makemake’s 2005 discovery. While the dwarf planet’s surface appears very bright and cold in infrared observations, certain regions register as warmer than others.
Scientists previously thought these regions were dark areas warmed by the Sun, which should have shown up as variations in surface brightness. However, no such variations were detected. The warmer areas previously detected in the infrared may instead be the surface of MK 2.
The striking contrast between bright Makemake and the dark moon could be due to MK 2 being too small to gravitationally maintain a hold on its icy crust once that crust sublimates directly to gas when hit by sunlight. This could be the same reason that comets and many tiny Kuiper Belt Objects are also very dark.
Video courtesy of NASA Goddard
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.