The Spitzer Legacy

Study of the universe, in all its majesty and wonders, has been one of the most fascinating areas of science for us humans, dating back to cavemen. Finding out more about the universe and understanding its origins has transformed from an unscientific procedure to one of the most scientifically complicated ones. The only way we can find out more about the universe is by using light, the only thing which reaches us from its distant residents. However, the visible part of the electromagnetic spectrum, the light we see, is only a tiny portion of the entire amount of light that we get from the universe. A great wealth of information about the universe comes to us in regions of the spectrum other than visible light. Keeping this in mind, NASA put forward its “Great observatories program”, which is basically four powerful telescopes to be put in space, each of which observes the universe in a different part of the EM spectrum!

The great observatories program consists of the following – The Compton gamma ray observatory, Chandra X-Ray observatory, Hubble Space telescope and the Spitzer Space telescope. Hubble, observes in our visible band of spectrum and the Spitzer, in the Infrared region.

Why infrared?

Infrared telescopes can detect objects too cool (and therefore too faint) to be observed in visible light, such as planets, some nebulae and brown dwarf stars. Also, infrared radiation has longer wavelengths than visible light, which means it can pass through astronomical gas and dust without being scattered. Thus, objects and areas obscured from view in the visible spectrum, including the centre of the Milky Way, can be observed in the infrared.

What is Spitzer?

The Spitzer Space Telescope was formerly known as the Space Infrared Telescope Facility. This telescope was launched on 25th August 2003. After more than 16 years studying the universe in infrared light, the mission was put to an end on January 30, 2020. The Spitzer is designed to detect IR radiation in the range of 3 microns and 180 microns. Spitzer’s prime mission ended in 2009, when the telescope ran out of its coolant, and then began to work in the warm phase. Because of no coolant, the detector couldn’t be maintained at the lowest possible temperature.  Among its many contributions, spitzer also studied comets and asteroids in our Solar System, and also discovered an unidentified ring around Saturn! Altogether, Spitzer observed 800,000 celestial targets and churned out more than 36 million raw images as part of its $1.4 billion mission.

Why Spitzer?

The ground based infrared telescopes have a major limitation. The water vapor in the atmosphere absorbs most of the low energy infrared radiation that we get, which is why the ground-based IR telescopes are at very high altitudes or in very dry deserts. Spitzer overcomes this easily as its in space, far from water vapor and also, away from the “thermal noise” of Earth itself.

Spitzer also follows what’s called an “Earth-Trailing orbit”. This means that Spitzer does not orbit the Earth. Instead, it drifts behind the Earth as it orbits the Sun. This is to further shield Spitzer from the ambient heat produced by the Earth itself. Spitzer, thus slowly drifts away from Earth at the rate of around 16,000,000 km per year.

The combined features of being a space IR telescope, being in deep space and having an Earth trailing orbit to shield it from ambient heat of Earth, means that despite being a small unit (only 0.85 m diameter mirror), Spitzer is far more powerful than any current IR telescope.

The findings of Spitzer

Spitzer has produced voluminous amounts of data, with new discoveries still being made by the analysis of the data generated. Some of the most notable discoveries made by the Spitzer telescope are :-

Discovery of a new ring around Saturn: – The Spitzer unveiled an entirely new ring around Saturn, one larger than any currently observed ring around the planet. This new ring is comprised of thin tenuous dust and ice particles. Because they are tiny and cool, they emit primarily in the infrared region, hence could be easily picked up by Spitzer. The new belt is at an angle of around 27 degrees from the main ring plane and extends outwards for roughly another 12 million kilometers. If this ring were visible in optical range, like the other rings, it could be distinguished by the naked eye from here on Earth!

The Trappist Exo-Planet system. : – Thanks to data from Spitzer and ground based telescopes, four more exo-planets were discovered around the cool red dwarf star Trappist-1. The interesting thing about them is they are all Earth sized and thus, caused quite a hype after their discovery, with three of these planets potentially around the Goldilocks zone of the star. Because the star itself is a dim red dwarf, usual methods of detection of exoplanets could not work and infrared telescopes did the job.

Hidden cradles of newborn stars: – Otherwise obscured by thick clouds of interstellar gas, Spitzer could easily peek through this and discover new areas of star formation, especially in the “Rho-Ophiuchi” dark cloud, one of the closest to our solar system.

Exoplanet weather map: – Spitzer using its infrared vision could map out the weather in the atmosphere of an exoplanet. The study revealed roaring winds in the planet’s atmosphere and for the first time, gave an insight into the atmosphere of an exoplanet.

What next?

The Spitzer mission has come to an end, providing us with a plethora of information, but its successor is already waiting to be launched. The James Webb Space Telescope, is a successor to the Hubble and Spitzer telescopes. Webb is about 1000 times more powerful than Spitzer and will be able to push Spitzer’s science findings to new frontiers, from identifying chemicals in the atmosphere of exoplanets, to discovering the first galaxies that formed after the Big Bang.

Rakshith Rao

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