Dozens of space-based telescopes operate near Earth and provide incredible images of the universe. But imagine a telescope in the outer Solar System, 10 or 100 times further away from the Sun than Earth. The ability to see our solar system or peek into the darkness of the distant universe would make it a uniquely powerful scientific tool.
I am an astrophysicist who studies the formation of structure in the universe. Since the 1960s, scientists like me have been pondering important scientific questions we can answer with telescopes in the outer Solar System.
So what would such a mission look like? And can science be done?
a small telescope away from home
The scientific power of a telescope away from Earth will come primarily from its location, not its size. Plans for a telescope in the outer solar system would place it far beyond the orbit of Saturn, about a billion or more miles from Earth.
We would only need to send a very small telescope – with a lens roughly the size of a small plate – to gain some truly unique astrophysics insights. Such a telescope could weigh less than 20 pounds (9 kg) and could be piggybacked on any mission to Saturn or beyond.
Although smaller and simpler than telescopes such as the Hubble or James Webb, such an instrument operating away from the Sun’s bright light can make measurements that are difficult or outright impossible from a vantage point near Earth.
Unfortunately for astronomers, taking a selfie of the solar system is a challenge. But being able to view the Solar System from an external vantage point will reveal a lot of information, especially about the size, distribution and composition of the dust cloud around the Sun.
Imagine a street lamp on a foggy evening – standing far away from the lamp, the swirling mist appears in a way that no one standing under the street light can ever see.
For years astrophysicists have been able to take and study images of dust disks in the Solar System around other stars in the Milky Way. But these stars are far away, and there is a limit to what astronomers can learn about them. Using observations looking at the Sun, astronomers can compare the size, characteristics and composition of these distant dust clouds with detailed data from Earth’s own solar system. This data will fill in the knowledge gap about solar dust clouds and make it possible to understand the history of dust production, migration and destruction in other solar systems that there is no hope of traveling individually.
Another advantage of placing binoculars away from the Sun is the reduction of reflected light. The disc of dust in the plane of the planets reflects sunlight back to Earth. This creates a haze that is 100 to 1,000 times brighter than light from other galaxies and obscures views of the universe from near Earth. Sending a telescope outside this dust cloud will bring it into a much deeper region of space, making it easier to measure light coming from outside the solar system.
Once there, the telescope can measure the brightness of the universe’s ambient light over a wide range of wavelengths. This could provide insight into how matter first condensed into stars and galaxies. This will enable researchers to test models of the universe by comparing the estimated amount of light from all galaxies with precise measurements. The discrepancies could point to problems with models of structure formation in the universe, or perhaps to exotic new physics.
in the unknown
Finally, increasing the telescope’s distance from the Sun allows astronomers to do unique science that takes advantage of an effect called gravitational lensing, in which a massive object distorts path light as it moves through an object.
One use of gravitational lensing is to find and weigh rogue planets – planets that roam interstellar space after being ejected from their home solar system. Since rogue planets do not emit light on their own, astrophysicists can look for their effect on light from background stars. Distinguishing between the lensing object’s distance and its mass requires observation from another location far from Earth.
In 2011, scientists used a camera on the EPOXI mission to the asteroid belt to discover and weigh a Neptune-sized object floating among stars in the Milky Way. Only a few rogue planets have been found, but astronomers suspect they are very common and may hold clues to the formation of the Solar System and the prevalence of planets around stars.
But perhaps the most interesting use for a telescope in the outer Solar System would be its ability to use the Sun’s gravitational field as a giant lens. This type of measurement could allow astrophysicists to actually map planets in other star systems. Perhaps one day we will be able to name the continents around a distant star on an Earth-like planet.
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Since Pioneer 10 became the first man-made object to cross Jupiter’s orbit in 1973, only a small number of astrophysical studies have been conducted beyond Earth’s orbit. Missions to the outer solar system are rare, but several teams of scientists are conducting studies to show how an extrasolar telescope project would work and what can be learned from one.
Every 10 years or so, leaders in the fields of astrophysics and astronomy gather to set goals for the next decade. That plan for 2020 is scheduled to be released on November 4, 2021. In it, I hope to see a discussion about the next telescope that could revolutionize astronomy. Taking a telescope to the outer Solar System, while ambitious, is well within the technical capability of NASA or other space agencies. I hope that one day soon a small telescope on a solitary mission into the dark reaches of the Solar System will give us incredible insight into the universe.