Kerberos (moon)
On the 28th of June 2011, researchers using the Hubble Space Telescope spotted a faint point of light near Pluto. This discovery came during an attempt to find rings around the dwarf planet that might endanger the New Horizons spacecraft. The team used the Wide Field Camera 3 to capture images over eight-minute exposures. Earlier observations had used shorter exposures and missed this object entirely. Kerberos appeared as only about 10% as bright as another moon named Nix. Further observations on the 3rd and the 18th of July 2011 confirmed its existence. Scientists later found it in archival images from February 2006 and June 2010 but diffraction spikes obscured it then. The International Astronomical Union officially designated it S/2011 (134340) 1 while the public called it P4.
Images from the New Horizons mission revealed Kerberos has a double-lobed shape unlike any other known moon. The larger lobe measures approximately 8 kilometers across while the smaller lobe spans roughly 4 kilometers. This unusual form suggests two smaller objects merged together long ago. Before the flyby scientists thought the moon was larger and covered in dark material. High reflectivity or albedo indicates water ice exists on the surface. The brightness matches that of Pluto's other small moons like Nix and Hydra. The double-lobed structure likely formed when debris coalesced around Pluto after a massive collision. This process mirrors theories about how Earth's Moon originated billions of years ago.
Kerberos does not keep one face toward Pluto as most large moons do. Its rotation is chaotic and varies quickly over geological timescales. Gravitational influences from both Pluto and Charon cause this tumbling motion. At the time of the July 2015 flyby the rotational period lasted about 5.33 days. The rotational axis tilted approximately 96 degrees relative to its orbit. This high axial tilt meant the moon rotated sideways compared to its path around the barycenter. Such behavior distinguishes it from tidally locked satellites found elsewhere in the solar system. The constant gravitational tug-of-war keeps the spin unpredictable and complex.
Observations show Kerberos follows a circular equatorial orbit around the Pluto-Charon barycenter. It travels at a distance of roughly 48,000 kilometers from the center point. All of Pluto's moons including Kerberos maintain very low orbital inclinations to Pluto's equator. The satellite completes one full revolution every 32.167 days. This timing creates a specific relationship with Charon known as a 1:5 orbital resonance. The discrepancy between perfect resonance and actual timing amounts to only 0.7%. Similar near resonances exist for Nix and Hydra which orbit at ratios of 1:4 and 1:6 respectively. Determining how close these relationships are requires more accurate knowledge of precession rates.
The New Horizons spacecraft captured images of Kerberos during its flyby on the 14th of July 2015. Three months later on the 22nd of October the first image reached the public. It was the last moon of Pluto to have its picture released to observers worldwide. The photograph showed a small body with a bright surface contrary to initial expectations. Scientists had previously believed the moon might be covered in dark material instead. The high resolution data allowed researchers to measure dimensions and study surface features directly. This encounter provided the first clear view of the double-lobed structure visible today.
Upon discovery the object received the minor planet designation S/2011 (134340) 1. Mark Showalter and the SETI Institute conducted an Internet poll in 2013 to choose names for P4 and P5. William Shatner proposed Vulcan after tweeting about it while Cerberus came second in popularity. The International Astronomical Union rejected Vulcan because it referred to a hypothetical planet inside Mercury's orbit. They also declined Cerberus since that name belonged to asteroid 1865 Cerberus. The Greek form Kerberos won approval from the IAU on the 2nd of July 2013. Features on the satellite must now relate to dogs from literature or mythology.
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Common questions
When was the moon Kerberos discovered by researchers using the Hubble Space Telescope?
Researchers spotted the moon Kerberos on the 28th of June 2011 during an attempt to find rings around Pluto. Further observations confirmed its existence on the 3rd and the 18th of July 2011.
What is the physical shape and size of the moon Kerberos according to New Horizons images?
Images from the New Horizons mission revealed that the moon Kerberos has a double-lobed shape with one lobe measuring approximately 8 kilometers across and another spanning roughly 4 kilometers. This unusual form suggests two smaller objects merged together long ago after debris coalesced around Pluto following a massive collision.
How does the rotation of the moon Kerberos differ from other moons in the solar system?
The moon Kerberos exhibits chaotic rotation rather than keeping one face toward Pluto like most large moons do. Its rotational period lasted about 5.33 days at the time of the July 2015 flyby while its axis tilted approximately 96 degrees relative to its orbit.
What are the orbital characteristics and resonance details for the moon Kerberos around Pluto?
The moon Kerberos follows a circular equatorial orbit at a distance of roughly 48,000 kilometers from the center point of the Pluto-Charon barycenter. It completes one full revolution every 32.167 days creating a specific relationship known as a 1:5 orbital resonance with Charon.
When did scientists first release images of the moon Kerberos to the public after the New Horizons flyby?
Scientists released the first image of the moon Kerberos to the public on the 22nd of October three months after the spacecraft captured data during its flyby on the 14th of July 2015. This photograph showed a small body with a bright surface contrary to initial expectations that it might be covered in dark material.
On what date was the name Kerberos officially approved by the International Astronomical Union for the moon P4?
The Greek form Kerberos won approval from the International Astronomical Union on the 2nd of July 2013 after rejecting other proposals like Vulcan and Cerberus. Features on the satellite must now relate to dogs from literature or mythology under this official designation.