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The king is dead - long live the king

Submitted by Kevin Jardine on 14 May, 2009 - 16:21

This has been an amazing week for those interested in space telescopes.

As I write this, the Hubble telescope has been lowered into a bay of the Shuttle Atlantis and is being re-equipped for another five-year mission. Seconds ago, the Herschel/Planck teams reported successful activation signals from those two observatories. And, more sadly, the Spitzer infrared telescope has finally run out of coolant after almost six years of wildly successful operation, reducing it to two frequencies from one instrument.

Although the two observatories are different in detail, the Herschel infrared telescope is the natural successor to Spitzer and it is an enormous relief to know (fingers crossed) that the Herschel mission is also on track for success. Herschel is by far the largest space telescope ever launched. As the Herschel website points out:

The telescope's primary mirror is 3.5 m in diameter, more than four times larger than any previous infrared space telescope and almost one and a half times larger than that of the Hubble Space Telescope. The telescope will collect almost twenty times more light than any previous infrared space telescope.

The infrared space telescopes (especially IRAS, MSX and Spitzer) have arguably been more important to mapping our Milky Way than any other scientific instrument. These instruments have been wildly successful in piercing through obscuring dust and giving us a view of our home galaxy that no telescope operating at optical frequencies could ever do.

I can only hope that Herschel will contribute much to this great tradition. This is already a bit of doubt unfortunately, ironically because of the power of the instrument. IRAS, MSX and Spitzer all made large surveys (respectively of the whole sky, the galactic plane, and the inner galaxy). Surveys are essential for mapping the Milky Way and discovering new objects. Because of Herschel's size, there may be a temptation to use it only for examining known objects more closely rather than doing larger surveys. Spitzer team member Barbara Whitney hinted at this when she said:

I suspect that Spitzer's view of the galaxy is the best that we'll have for the foreseeable future. There is currently no mission planned that has both a wide field of view and the sensitivity needed to probe the Milky Way at these infrared wavelengths.

Let's hope that Herschel's greater power does indeed allow it to make an even greater contribution to science than the infrared telescopes that have come before.