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.
Ganymede, the largest moon of Jupiter, is a water world.
Researchers using the Hubble Space Telescope have confirmed an ocean beneath Ganymede’s icy crust that are likely ten times deeper than Earth’s oceans.
The moon may have more liquid water beneath its surface than there is on Earth.
To reach this conclusion, scientists measured fluctuations in the moon’s aurorae. Aurorae, which are electrified ribbons of heated gas, are generated when a planetary body’s liquid metal core produces a magnetic field.
On Ganymede, the aurorae around its north and south poles move, influenced by fluctuations in Jupiter’s huge magnetic field.
Scientists used computer modeling to verify that the only explanation for the extent of the “rocking” of Ganymede’s aurorae is the presence of a saline ocean, which would cause Ganymede’s magnetic field to offset to some extent Jupiter’s magnetic impact.
Several measurements indicated that the aurorae moved by about two degrees, but without the presence of an ocean Jupiter’s influence would have caused movement of about six degrees.
“When there is an electrically conductive ocean present, this counteracts Jupiter’s influence,” Joachim Saur, a professor geophysics at Germany’s University of Cologne and the lead researcher, said.
Saur explained that four independent measurements with HST verified the two-degree movement of Ganymede’s aurorae.
Scientists had speculated for several decades that Ganymede could be an oceanic moon. The Galileo probe, which flew by the moon several times during its 1995-2003 mission, provided further grist for that supposition when it measured the moon’s magnetic field. But those flybys did not last long enough for scientists to detect the movement of Ganymede’s aurorae.
“The flybys lasted only 20 minutes each,” Saur said. “In the new Hubble observations we have seven hours of data, so we do not have the ambiguity anymore.”
Ganymede’s sea may also be impacting the surface of the moon. Mapping of the satellite by the U.S. Geological Survey reveals areas of the surface that are smoother and less cratered than other areas, which could indicate the presence of tectonic forces that permit movement of sea water from beneath the icy crust.
“These lighter shaded regions are believed to be formed by flooding on the surface by water coming to the surface by faults or even cryovolcanoes,” Jim Green, NASA’s director of planetary science, said.
Ganymede is Jupiter’s largest moon, with more mass than Mercury. It joins fellow Galilean moon Europa and Saturn’s moon Enceladus on the list of moons known to have water oceans.
Another of Jupiter’s four largest moons, Callisto, is also thought likely to have liquid water.
“Every observation that we make, every mission that we send to various places in the solar system, is taking us one step closer to finding that truly habitable environment, a water-rich environment in our solar system,” Heidi Hammel, executive vice president of the Association of Universities for Research in Astronomy, said. “Everywhere we look there’s water.”
Two newly-discovered moons of Pluto now have names.
The International Astronomical Union announced Tuesday that the fourth and fifth satellites of the solar system’s former ninth planet will be known as Kerberos and Styx.
Like moons of most of Earth’s other planetary neighbors, the names relate to the gods of Greek and Roman mythology.
Kerberos is the name of the dog that guards the underworld in the ancient Greek tales, while Styx is the name of the river that separated Earth and the underworld in those tales.
Both moons are recent discoveries.
“They were both discovered in images from the Hubble Space Telescope,” Mark Showalter, an astronomer associated with the Carl Sagan Center for Study of Life in the Universe at California’s SETI Institute and the leader of the research team that discovered them, said. “P4, which is now Kerberos, was found in 2011, late June or July, and P5 was found about this time in 2012. The discovery of P4 was actually in a short Hubble program to search for dust rings around Pluto. We were doing that by taking longer exposures of Pluto than anyone had attempted before.”
Researchers subsequently decided to look for more evidence of additional satellites of Pluto.
The two moons are very small, on the order of about 100 times smaller than Charon, Pluto’s largest satellite.
“They’re just dots in the sky,” Showalter explained. “The estimates we have are on the order of 10-15 miles in diameter. Three billion miles away, and that’s how big they are. Just to illustrate, P5 is about 100,000 times fainter than Pluto itself. They’re separated on the sky by, basically, a hair’s breadth.”
Charon has a diameter of about 1,200 kilometers.
Kerberos and Styx almost certainly move in synchronous rotation with Pluto, just as Earth’s moon does in relation to our planet.
“Every satellite in the solar system, except Saturn’s moon Hyperion, has been shown to be tidally locked,” Showalter said.
The Hubble Space Telescope was used to find Pluto’s two other known satellites, Nix and Hydra, in 2005. Those moons are named, respectively, for the Greek goddess of darkness and night and the nine-headed serpent that fought Hercules in the ancient myths.
The system of naming moons for characters of Greek and Roman mythology is commonly employed by astronomers in naming the moons of the solar system’s planets.
“Moons of Neptune are named for creatures associated with the oceans in Greek and Roman mythology because Neptune was the god of the ocean,” Showalter said.
Similarly, eight moons of Saturn are named for titans of Greek mythology, while many of Jupiter’s moons – notably excluding Callisto, Europa, Ganymede, and Io – are named for lovers and descendants of Zeus. Mars’ two moons are named for children of Ares, the Greek god of war.
The moons of Uranus are named for characters from English literature, particularly Shakespeare’s plays.
Kerberos and Styx may not be the last moons of Pluto to be discovered. The New Horizons spacecraft is scheduled to arrive in the vicinity of Pluto in 2015, allowing scientists a close-up look at the dwarf planet and its satellites.
“I would be frankly surprised if we don’t find a P6 and a P7 and a P8,” Showalter said. “Whatever is going on in the Pluto system that created this family of moons probably didn’t stop at five.”
He explained that it’s not likely the IAU will have any problem finding names for any newly-discovered Plutonian moons that fit the existing theme.
“I can assure you that is not a concern,” Showalter said. “We had 30,000 write-in candidates put in. There’s a long list. I still have that list. I’d like to think we’ll be returning to that list come 2015 when we find other rocks out there.”
Graphic courtesy Wikimedia
The moon, which has been labeled P4, joins Charon, Hydra, and Nix among the known celestial bodies around the solar system’s former ninth planet.
“This is a fantastic discovery,” Dr. S. Alan Stern, an associate vice president of the Southwest Research Institute in Boulder, said. “Now that we know there’s another moon in the Pluto system, we can plan close-up observations of it during our flyby.”
Stern was referring to NASA’s New Horizons mission, which will arrive in the vicinity of Pluto in 2015. He is the principal investigator for that mission.
P4, whose orbit is located between those of Hydra and Nix, was first seen in images captured by a wide-field camera on the telescope June 28.
Astronomers noticed it while they were looking for evidence that Pluto has rings. To find out whether it does, the scientist need to deploy a camera that is capable of detecting very dim objects deep in space.
Pluto is about 3 billion miles from Earth.
Stern said that no rings have yet been found around Pluto.
“But that doesn’t mean there are not rings around Pluto,” he cautioned.
The discovery of P4 was confirmed in two other photographs taken by a camera on the Hubble this month.
Pluto’s other moons are much larger than P4.
Charon, the largest, is 648 miles across, while Hydra and Nix each have a diameter of 20-70 miles.
Hydra and Nix were discovered through use of the Hubble Space Telescope in 2005.
Charon was first discovered by astronomers at the U.S. Naval Observatory in 1978.
Scientists believe that Pluto’s moons were created when another celestial object collided with the dwarf planet during the early history of the solar system.
“The object that collided with Pluto and created its satellite system was probably about 1000 kilometers across, maybe somewhat larger,” Stern said.
The newly-discovered moon will receive a permanent moniker at a later date.