Makemake, a dwarf planet far beyond Pluto in the Kuiper Belt, has a moon.
Imagery obtained by the Hubble Space Telescope detected the satellite last April, according to a recently published paper.
The moon, which has been temporarily catalogued as S/2015 (136472) 1 and nicknamed MK2, is about 100 miles in diameter. It was observed orbiting Makemake from a distance of about 13,000 miles.
MK2 probably orbits Makemake in an orientation that makes it difficult for astronomers to observe the moon.
“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,” Dr. Alex H. Parker, a planetary scientist at Southwest Research Institute in Boulder, Colo., said.
Parker led the team that analyzed the Hubble image of MK2.
One implication of the Makemakean moon’s discovery is an increased ability to measure Makemake’s mass and density.
To measure the dwarf planet’s mass, scientists will need to overcome the challenges inherent in observing MK2’s orbit. If they succeed in doing so, and because the distance from Earth to Makemake is already known, it would be possible to use the orbital period and the mean distance of MK2 from Makemake to determine Makemake’s mass.
To determine Makemake’s density, scientists must know its volume, which in turn requires knowledge of the dwarf planet’s diameter. Makemake’s diameter is about 1,500 kilometers.
Once the volume is determined, density can be calculated by dividing Makemake’s mass by its volume.
Astronomers used a camera on the Hubble Space Telescope to find MK2. That instrument, called Widefield Camera 3, is able to capture images across the radiation spectrum.
Widefield Camera 3 has a 16 megapixel capacity and can capture an image as large as 160 arcseconds by 160 arcseconds in size.
Makemake is the second-brightest object, after Pluto, in the Kuiper Belt and is, like Pluto, covered with methane ice.
The dwarf planet, which was discovered in 2005, is named for a deity that is worshiped by native people of Easter Island.
In addition to Makemake, there are four other dwarf planets in the solar system: Pluto, Eris, Haumea, and Ceres.
With the discovery of MK2, astronomers now know that all of the solar system’s dwarf planets have moons.
Scientists have discovered water vapor on Ceres, a dwarf planet and the largest object in the asteroid belt.
Using the European Space Agency’s Herschel space telescope, researchers detected a spectral signature of the substance on four occasions.
“This is the first time water vapor has been unequivocally detected on Ceres or any other object in the asteroid belt and provides proof that Ceres has an icy surface and an atmosphere,” Michael Kueppers, a planetary scientist at ESA and the lead author of a paper documenting the discovery, said.
Ceres is an ice-covered object. One way the water vapor could have formed is through the melting of that ice as Ceres moves closer to the sun during its orbit.
“Think of it as ice that has been covered by dust,” Joel W. Parker, a planetary scientist at Southwest Research Institute in Boulder, Colo. who has studied Ceres, said. “That ice heats up as Ceres slightly gets closer to the sun. The ice sublimates, goes to gas, lifts off some of the dust, which perhaps exposes a little more ice.”
Parker said that the other possible mechanism for melting Ceres’ ice could be cryo-volcanism.
“Ceres is layered, kind of like the Earth,” he said. “Ceres has ice. If there is some deeper ice, there could be cryo-volcanism.”
Cryovolcanos occur on frozen celestial objects and involve the eruption of volatile compounds, including water, in plumes.
“You need to heat that mantle somehow to make the water escape, to make the low volcanoes,” Parker explained. “You can’t do that with heat from the sun. That model would require internal heating, like some radioactive elements.”
Kueppers and his fellow researchers concluded that the ice melt scenario is more likely correct.
It will not be necessary to wait long for a conclusive determination about whether their conclusion is the right one. NASA’s Dawn probe is in the asteroid belt and is scheduled to arrive at Ceres next spring.
The spacecraft has on board both a visible and infrared mapping spectrometer and a gamma ray and neutron detector.
“We first hope to see surface markings that will tell us where the vents, if any, are,” Christopher Russell, the DAWN mission’s principal investigator and the director of the Institute of Geophysics and Planetary Physics at the University of California at Los Angeles, said. “They should be able to tell whether there are water-bearing minerals with the mapping spectrometer. The neutron detector will tell us where there is hydrated soil.”
Scientists have long been confident that Ceres is shrouded in ice. Spectroscopic observations of the dwarf planet have indicated that it has a silicate core. Since the total density of Ceres and the assumed density of the silicate core can be calculated, Ceres’ mantle must be composed of several tens of kilometers of ice.
“We always expected Ceres to be a wet body because of its low density,” Russell said.
Kueppers and his colleagues detected a huge amount of water vapor sublimating from Ceres. About one octillion molecules of the compound are moving into space each second.
They appear to emanate from the dwarf planet’s mid-latitudes.
Ceres was discovered by the Italian astronomer Giuseppe Piazzi on Jan. 1, 1801. It was initially thought to be a planet with an orbit that lay between Mars and Jupiter, but soon after its discovery was deemed an asteroid. It was reclassified as a dwarf planet in 2006 because of its 950 kilometer diameter, large for an asteroid belt object.
The paper appears in the Jan. 23 edition of Nature.
This image of Ceres was obtained by the Hubble Space Telescope on Jan. 1, 2004. Image courtesy NASA, European Space Agency, Southwest Research Institute, Cornell University, University of Maryland, and Space Telescope Science Institute.