Cosmic Background Explorer: COBE

What is COBE The Cosmic Background Explorer (COBE) was also referred to as Explorer 66 Satellite dedicated to cosmology Its goals were to investigate the cosmic microwave background radiation (CMB) of the universe and provide measurements that would help shape our understanding of the cosmos.

What is CMB Cosmic background radiation: (cosmology) the cooled remnant of the hot big bang that fills the entire universe and can be observed today with an average temperature of about 2.725 kelvin

Launch COBE was originally planned to be launched on a Space Shuttle mission STS-82-B in 1988, but the Challenger explosion delayed this plan when the Shuttles were grounded. COBE was placed into sun-synchronous orbit on November 18, 1989 Launched From: Vandenberg Air Force Base Launch Vehicle: Delta 5000

Instruments Differential Microwave Radiometer (DMR): microwave instrument that would map variations in the CMB Far-Infrared Absolute Spectrophotometer (FIRAS): spectrophotometer used to measure the spectrum of the CMB Diffuse Infrared Background Experiment (DIRBE): multiwavelengh infrared detector used to map dust emission

COBE COBE was an Explorer class satellite, with technology borrowed heavily from IRAS, but with some unique characteristics. The need to control and measure all the sources of systematic errors required a rigorous and integrated design. COBE would have to operate for a minimum of 6 months, and constrain the amount of radio interference from the ground, COBE and other satellites as well as radiative interference from the Earth, Sun and Moon. The instruments required temperature stability and to maintain gain, and a high level of cleanliness to reduce entry of stray light and thermal emission from particulates.

Scientific Findings The science mission was conducted by the three instruments: DIRBE, FIRAS and the DMR. The instruments overlapped in wavelength coverage, providing consistency check on measurements in the regions of spectral overlap and assistance in discriminating signals from our galaxy, solar system and CMB. COBE's instruments would fulfill each of their objectives as well as making observations that would have implications outside of COBE’s initial scope. The famous map of the CMB anisotropy formed from data taken by the COBE spacecraft.

Black-body Curve Data from COBE showed a perfect fit between the black body curve predicted by big bang theory and that observed in the microwave background. The results of FIRAS were startling in that they showed a perfect fit of the CMB and the theoretical curve for a black body at a temperature of 2.7 K

Intrinsic Anisotropy The DMR was able to spend 4 yrs mapping the detectable anisotropy of cosmic background radiation. This operation was able to create full sky maps of the CMB The cosmic microwave background radiation is a remnant of the Big Bang and the fluctuations are the imprint of density contrast in the early universe. The density ripples are believed to have produced structure formation as observed in the universe today: clusters of galaxies and vast regions devoid of galaxies.

Detecting early galaxies DIRBE also detected 10 new far-IR emitting galaxies in the region as well as nine other candidates in the weak far-IR that may be spiral galaxies. Galaxies that were detected at the 140 and 240 μm were also able to provide information on very cold dust (VCD). At these wavelengths, the mass and temperature of VCD can be derived. When these data were joined with 60 and 100 μm data taken from IRAS, it was found that the far-infrared luminosity arises from cold dust associated with diffuse HI cirrus clouds, 15-30% from cold dust associated with molecular gas, and less than 10% from warm dust in the extended low-density HII regions.

DIRBE The DIRBE instrument was able to conduct studies on interplanetary dust(IPD) and determine if its origin was from asteroid or cometary particles. The DIRBE data collected at 12, 25, 50 and 100 μm were able to conclude that grains of asteroidal origin populate the IPD bands and the smooth IPD cloud.

DIRBE The second contribution DIRBE made was a model of the Galactic disk To create this model, the IPD had to be subtracted out of the DIRBE data. It was found that this cloud, which as seen from Earth is Zodiacal light, was not centered on the Sun, as previously thought, but on a place in space a few million kilometers away. This is due to the gravitation influence of Saturn and Jupiter.

Conclusion Two of COBE's principal investigators, George Smoot and John Mather, received the Nobel Prize in Physics in 2006 for their work on the project.

References wordnetweb.princeton.edu/perl/webwn http://www.bbc.co.uk/science/space/universe/exploration/cosmic_background_explorer Understanding Our Universe by Palen, Kay, Smith, Blumenthal http://en.wikipedia.org/wiki/Cosmic_Background_Explorer#Spacecraft http://solarsystem.nasa.gov/missions/profile.cfm?Sort=Target&Target=Mars&Era=Present http://lambda.gsfc.nasa.gov/product/cobe/ http://www.scholarpedia.org/article/Cosmic_background_explorer_(COBE)