Big science on the ISS

What science experiment is so large that it will get its own Shuttle flight in July 2010?  At nearly 15,000 lbs, that would be the Alpha Magnetic Spectrometer, flying on STS-134/ULF6.

After the cancellation of the Superconducting Super Collider (which would have been based in Texas), MIT Nobel laureate and physicist Samuel Ting proposed putting a cosmic ray detector on the Space Station to help look for such things as dark matter and antimatter.

A prototype detector was flown on the Shuttle in 1998 as a proof-of-concept.  Though it did not detect such exotic materials such as antihelium, AMS-01 demonstrated that we could successfully fly a particle detector in space.  AMS-02 is the full-scale version that will be mounted externally on the Space Station’s truss.  Because it will operate continuously for at least three years, AMS-02 will have the time necessary to detect the rare and sparse particles and cosmic rays that will give us deeper insights into the formation of the universe.

AMS is a project involving over 500 scientists from 56 institutes in 16 countries, built by CERN in Geneva, Switzerland, and sponsored by the Department of Energy.  The detector uses a huge cryogenic superconducting magnet to capture cosmic rays and particles and bend their paths towards a series of detectors that will measure their size, orientation, position, velocity, charge, and energy levels.  The AMS is capable of detecting gamma rays, electrons, positrons, and various charged nuclei.

Additionally, as this is the first experiment with a large superconducting magnet in space, the AMS team will investigate the principles behind the possibility of using magnetic shielding for manned deep space missions.  Current estimates of radiation exposure on a manned mission to Mars far exceed the career limits for astronauts set by the various space agencies.  We will need a solution to the problem of radiation exposure if we are to eventually send people to explore the Red Planet and beyond.  AMS may be the first step in finding such a solution.

However, that is more of an engineering problem than a science problem.  The primary scientific goals of the AMS experiment are to search for antihelium nuclei, examine the positron spectrum, search for strangelets, study cosmic and gamma rays, and look for the exotic byproducts of primordial black holes.  But what is so important about those goals?

Antihelium nuclei are important because our observations of the universe suggest there are large regions dominated by antimatter.  The detection of antihelium, which does not commonly form in “normal” particle collisions, would help confirm that theory and refine our models of the universe.

We want to study the positron spectrum to see if there are a large amount of high-energy positrons.  Known positron sources tend to emit at relatively low energies, but we think a certain kind of dark matter – the neutralino – decays into high-energy positrons.  If we find a lot of them, then we’ll know that neutralinos are likely to represent a significant portion of dark matter.

Strangelets are another possibility for what dark matter is.  They are hypothetical particles heavier and more stable than normal matter, but that require a higher level of energy to form.  If we can detect strangelets, we’ll have a better idea of the processes that occurred at the beginning of the universe and high-energy processes happening now.

By studying the spectra of cosmic rays and the resultant ratio of certain elements, we can determine where they came from and how old they are. Again, this will give us further insights into the high-energy processes of the universe, like supernovas and black holes.

Speaking of black holes, some scientists are hoping that AMS will detect the remnants of what are called primordial black holes.  While most black holes form from the collapse of massive stars, these formed under the extreme heat and pressure during the first few moments after the Big Bang.  Physicist Stephen Hawking has theorized that black holes emit thermal radiation due to quantum effects, slowly evaporating away their mass.

The AMS might be able to detect the “Hawking radiation” emitted from these ancient black holes.  If so, scientists would gain tremendous insight into the density fluctuations in the early universe.  In conjunction with the Fermi Gamma-Ray Telescope launched last year, this might also give us the first evidence for string theory – which proposes that there is actually a fourth spatial dimension!

Whew, that’s a lot!  We’re talking Nobel Prize-level fundamental physics research here.

Here’s a video of what the AMS-02 installation will look like.  Once on orbit and docked at the ISS, the Shuttle Remote Manipulator System will hand off AMS to the Space Station’s robot arm (SSRMS).  The SSRMS will place the particle detector on its dedicated site on the Station’s truss.

Cross-posted at Cosmo.Sphere