The Comet C/2013 A1 Siding Spring was discovered on 3 January 2013 by R. McNaught, and it is of great interest to scientists as it may hold clues to the formation of the solar system. This comet is believed to be making its first ever visit to the inner solar system.
What’s particularly unusual about this comet is that it will make a close approach to Mars on October 19, 2014, perhaps within 100,000 km, close to the comet’s perihelion. When the comet is near its greatest brightness and activity is also when it will pass so close to Mars that its atmosphere will collide with the atmosphere of Mars. The outcomes of this spectacular encounter will be studied by a flotilla of spacecraft around Mars and on the surface of Mars, as well as spacecraft and observatories on Earth.
But just a few weeks before Comet Siding Spring makes close approach to Mars, NASA will launch a special stratospheric balloon – the Balloon Observation Platform for Planetary Science (BOPPS) – carrying a 0.8 m aperture telescope and optical and infrared sensors to study the comet from above 99.5% of Earth’s atmosphere. BOPPS will observe Comet Siding Spring in the near-infrared and in the near-ultraviolet and visible wavelength ranges, from an altitude of 120,000 to 130,000 feet.
There is another bright comet that BOPPS will observe in its one day flight, which is Comet C/2012 K1 PanSTARRS, discovered on 17 May 2012 using the PanSTARRS telescope in Hawaii. It is, like Siding Spring, an Oort Cloud comet on its first visit to the inner solar system.
The atmosphere is opaque at the light wavelengths that scientists want BOPPS to measure, which means those measurements are not possible from the ground. BOPPS will observe Comets Siding Spring and PanSTARRS in the near-infrared from 2.5 to 5 microns and in the near-ultraviolet and visible wavelength ranges from 300 nm to 850 nm.
The BOPPS instrument payload comprises two instruments on separate optical benches: the BOPPS Infrared Camera (BIRC), for photometric imaging from 2.5 to 5.0 um, and a near-ultraviolet and visible imaging system (UVVis) with a fast steering mirror and fine guidance for obtaining sub-arcsec pointing stability. BIRC was developed by the Johns Hopkins Applied Physics Laboratory. UVVis was developed by the Southwest Research Institute.
The primary science objectives of the BOPPS mission are to measure CO2 and H2O emissions from the Oort Cloud Comets C/2013A1 Siding Spring and C/2012K1 PanSTARRS. These are unique observations that cannot be obtained by any other means. The near ultraviolet and visible UVVis camera will observe at the wavelength of the hydroxyl (OH) emission from Comet Siding Spring and will test and characterize the effects of atmospheric turbulence on optical observations at balloon altitudes. The primary UVVis objective is to demonstrate image pointing stability well under an arc second.
In addition to observing the Comets Siding and Spring and PanSTARRS, scientists plan to have BOPPS observe many other targets during its flight. These include the dwarf planet 1 Ceres and the large asteroid 4 Vesta, as well as Uranus and Neptune. BOPPS will study water on Vesta and Ceres, which are targets of the NASA Dawn mission. Dawn has completed its orbital study of Vesta and will rendezvous with Ceres in April, 2015. BOPPS will also observe Uranus, Neptune, and depending on the actual launch day, Jupiter or the Moon.
BOPPS is the re-flight of the BRRISON mission. The BRRISON mission was a rapid response to the opportunity presented by the discovery of Comet C/2012 S1 ISON, providing a new planetary science platform to fly in the stratosphere within one year of the comet discovery. BRRISON encountered a flight anomaly and was not able to observe ISON.
Comets Siding Spring and PanSTARRS
The BOPPS primary science objective is to measure CO2 and H2O emissions, at 4.3 and 2.7 micron wavelengths respectively, from the Oort Cloud Comets Siding Spring or Panstarrs.
Where are the comets? The locations of the Comets Siding Spring and PanSTARRS projected onto the plane of Earth’s orbit (the ecliptic plane, viewed from the north) are shown in the figure. The Earth’s orbit is in blue, the Comet PanSTARRS is in red, and the Comet Siding Spring is in green. The numbers indicate the locations at particular dates, in the table to the right. Point 1 indicates the locations on June 1, 2014. Point 7 indicates locations at around the time of the BOPPS flight, on October 5, 2014, when the comet is almost at the position of Mars. Closest approach of Siding Spring to Mars occurs on October 19, between points 7 and 8. Both comets are retrograde comets, meaning that they move around the Sun (small yellow circle at the center) in the clockwise direction, whereas the Earth moves around its orbit in the counter-clockwise direction. Both comets are also in highly inclined orbits, far out of the plane of Earth’s orbit. Comet Siding Spring is far south of the ecliptic plane as it approaches the Sun (and Mars), crosses the ecliptic plane between points 7 and 8, and departs again to the north. Comet PanSTARRS approaches the Sun from far north of the ecliptic plane, crosses the ecliptic plane between points 4 and 5, and departs to the south. The black arrow indicates the zero of ecliptic longitude.
BRISSON will be built and managed by Johns Hopkins University Applied Physics Laboratory (JHU/APL) in collaboration with NASA’s Glenn Research Center (GRC), NASA’s Balloon Program Office (BPO), the Columbia Scientific Balloon Facility (CSBF) and the Southwest Research Institute (SwRI). APL will lead the design and integration of the payload with the gondola platform, as well as the technical aspects of the IR payload. SwRI will lead the technical aspects of the Visible/UV payload.