It has been almost 32 years since the Space Shuttle Discovery launched the Hubble Space Telescope into Earth orbit.
Since then, the school bus-sized scope has flown around the Earth at 17,000 miles per hour, observing distant nebulae, galaxies and, only occasionally, objects in its own solar system.
In fact, Hubble has only spent 6% of its time probing targets in the Solar System during its lifetime.
Even so, Hubble is vital to planetary scientists in a way the new James Webb Space Telescope (JWST) can never be.
Hubble broadcasts images of the giant planets, specifically Jupiter and Saturn, every year as part of its Outer Planets Atmospheres Legacy (OPAL) program so scientists can look for changes in their storms, winds and clouds.
As for the many smaller bodies in the outer Solar System, astronomers already have little time to study them with Hubble.
Glances once a year aren’t much, and besides, Hubble is getting old (and starting to fail). The new JWST will study something Targets in the solar system – like Jupiter’s “Great Red Spot” – but it will work mostly in the infrared, so it’ll be mostly focused on space. It’s primarily for astrophysics, not planetary science.
Either way, there may soon be no “eye in the sky” that could send us pictures of planets, comets, asteroids, and make new discoveries.
Imagine what planetary scientists could do with a telescope focused 100% on objects in the solar system.
Is it time for a special Solar System Space Telescope (SSST)?
What is the Solar System Space Telescope?
It is a large/medium space telescope dedicated to planetary exploration and observation of targets throughout the solar system. We are talking about high-resolution, highly sensitive observations in the visible and ultraviolet wavelength range.
This is currently possible from Hubble, but not from Webb, which sees primarily in the infrared.
All of this is detailed in a white paper now considered part of the forthcoming Decadal Survey of Planetary Science and Astrobiology, a report compiled by the National Academy of Sciences that will set NASA’s priorities for the next 10 years. It will be released on April 19, 2022.
The authors would like the SSST to be considered for one of NASA’s New Frontiers missions, which typically cost less than $1 billion. SSST is valued at $815 million.
Why do we need a solar system space telescope?
To help astronomers understand time-varying phenomena in our solar system — like seasonal changes on planets, dust storms, and even rare cometary impacts — as well as a detailed study (and a hunt for more) of smaller solar system bodies.
“What’s interesting about goals in the solar system is that on human timescales they are evolving — very rapidly — sometimes on a daily basis, but definitely on an annual basis,” said Kunio Sayanagi of Hampton University, Virginia, who co-authored the Proposal for the SSST. “Hubble’s OPAL program took a good view of Jupiter, Saturn, Uranus and Neptune once a year to see the changes.”
Sure, Juno on Jupiter and Cassini on Saturn took far higher resolution images during Hubble’s lifetime, but such missions don’t last long.
A solar system space telescope could examine:
- Volcanic activity on Venus and Titan, a large moon of Saturn.
- Look for water vapor on the moons of Uranus (Miranda and Ariel), Neptune’s massive moon Triton, and Pluto.
- The changing surfaces of Enceladus, a moon of Saturn, and Io, a volcanic moon of Jupiter.
- Study Jupiter’s Trojans, irregular satellites, centaurs, and Kuiper Belt Objects (KBOs).
Why can’t we use the Webb Space Telescope?
Webb is amazing. It has a 6.6-metre mirror – compared to the Hubble Space Telescope’s 2.4-metre mirror – which means six times the collection power.
However, we shouldn’t compare Webb to Hubble.
While the latter looks at the universe primarily in visible light, Webb is an infrared telescope. Webb’s sensitivity to infrared light means it can see light from the first stars – 300 times more massive than the Sun – and the faintest, earliest galaxies.
“JWST is not a successor in the strict sense that it would continue any of the measurements that Hubble made,” said Dr. Cindy L. Young, physics scientist at NASA Langley Research Center in Hampton, Virginia. Finally, there is little overlap in the wavelength domain. JWST’s shortest wavelength coverage is 700 nanometers, while Hubble drops to nearly 200 nanometers. So, in terms of wavelength, JWST is not a continuation of Hubble. “For the UV light measurements, which are so important for uncovering temporally dynamic phenomena in the solar system, we need high-frequency, long-duration missions,” Young said.
In short, JWST is simply not designed for planetary astronomy, but to answer astrophysics questions. Besides, there will be no more time. “The use of astrophysical resources for solar system science is important, but cannot fully address the science described here given the number and time-varying nature of solar system targets,” the paper states. JWST is for “first look” science, as is Hubble in general – neither telescope is designed to look at objects more than once.
However, Hubble will remain very valuable to planetary scientists until a successor – in terms of UV wavelengths – emerges.
Call up the SSST.
How big would the solar system space telescope be?
We are talking about a 10 meter telescope. Although different from the JWST, the SSST builds in some ways on the technologies developed for the JWST. Aside from being much less sensitive – because objects in the solar system are generally bright – it uses a sparse aperture design to get a really sharp, detailed image. No sun protection is required either. “We hope that it will be cheaper so that it can be built faster,” Sayanagi said.
The SSST is based on the concept of the Caroline Herschel High-Angular Resolution In-Space Assembly Multi-Aperture (CHARISMA) telescope.
What could a solar system space telescope do?
It could react to events on rapidly changing targets.
Take Europa, one of Jupiter’s largest moons, which is a prime target for astrobiology. “Hubble has looked at Europa a few times and it looks different each time, but there have been tantalizing signs that it’s spewing water into space,” Sayanagi said. However, Hubble is barely sensitive enough to return an interesting signal. “If we could look at Europa more often, we could see how often its plumes occur, where they occur on the surface, and see if they are associated with interesting geological features on its surface.”
Another area ripe for exploration by a space telescope, and largely overlooked, is small, cold, and dark bodies in the outer Solar System, which JWST may locate but will not have time to properly characterize. Some of these small bodies known to science have rings that have never been studied – and don’t forget the ring systems of Jupiter, Saturn, Uranus, Neptune.
There are many, many other uses for an SSST, such as auroras and weather systems on planets, and studies of asteroids and comets.
Why Venus is the perfect example of why we need a Solar System Space Telescope
Then there is Venus and Saturn’s moon Titan. “It’s still unclear whether there is active volcanism on Venus, so having more time to target it would help us answer that question,” Sayanagi said. How energy moves around Venus is important, scientists need to draw parallels with Earth’s weather as well as the atmospheres of exoplanets. But how long can JWST stare at Venus and Titan to observe how fast their clouds are moving, and therefore measure their wind speeds?
In the case of Venus, it’s actually a much more fundamental problem than pure observing time because JWST can do that never look somewhere near Venus. Hubble doesn’t typically look at Venus either — it’s generally far too close to the Sun.
“Looking at the Sun is dangerous business for telescopes, so you have to build in a special capability,” Young said, proposing a carefully designed optical aperture that will allow the SSST to close Venus and everything else within 30º of the Sun see.
The Hubble Space Telescope was great, but calling JWST its successor is a mistake. There threatens a great gap in our ability to study what is going on in our own solar system, which can only be filled by launching a space telescope dedicated to planetary research.
I wish you clear skies and big eyes.