Laser guide stars can help segmented space telescopes to explore the distant exoplanetary systems.

The idea of finding a habitat for humanity, other than the Earth, has grown rapidly in recent years. Astronomers have found thousands (about 4,000) of confirmed exoplanets in different parts of the universe. In addition to that, there is an abundance of potential candidates that need further research before concluding anything about their status. Most of these distant bodies are detected through their ‘Transits’ (an instance when a planet momentarily blocks the light of its star). Despite the fact that these events give some basic knowledge about the planet, a lot of vital information (traces of water and Oxygen) can be extracted through advanced tools.

Bigger telescopes with light-gathering mirrors offer an ideal solution in this regard. Scientists are now trying to design such telescopes. For example, Segmented telescopes will have a number of small mirrors that can be joined together to form a very large telescope once it is launched into space. The James Webb Space Telescope of NASA is a segmented primary mirror with 18 hexagonal segments. According to a report, engineers are designing the next-generation telescopes to cater as much as 100 segments. Having said that, it is easier said than done as several technicalities are attached to these telescopes.

One of the massive challenges faced by these segmented telescopes is to keep the segments stable and point them collectively towards an exoplanetary system. The idea is to equip the telescopes with Coronagraphs to determine the difference between the light emitted by the star and the light given off by an orbiting planet. The problem with this approach is that the slightest defect in a part of the telescope can affect the measurements of a coronagraph.

In order to solve this issue, the engineers from MIT proposed that assisting spacecraft should fly with these bigger telescopes. The sole responsibility of this spacecraft will be to act as a ‘guide star’ for the large telescope. It will do that by providing a steady, bright light (laser) near the target system, which will allow the telescope to keep itself stable. Recent research showed that the development of such a laser guide star is very much possible with today’s technology. Ewan Douglas, the Lead Author of the paper who works in the Department of Aeronautics and Astronautics at MIT, talked about the feasibility of this project by saying,

“This paper suggests that in the future, we might be able to build a telescope that’s a little floppier, a little less intrinsically stable, but could use a bright source as a reference to maintain its stability.”

Douglas mentioned that astronomers are using the actual stars as guides for ground-based telescopes for over a century now. Similarly, lasers were introduced as artificial guides in the 1990s. This procedure revolved around the excitation of Sodium in the upper atmosphere. This created a point of light at an approximate distance of 40 miles from the ground and scientists could then stabilize a telescope by using it. He also elaborated that space telescopes need to counter minute changes in temperature and any disturbances in motion to ensure the accuracy needed to perform exoplanet imaging. He talked about the importance of these large telescopes and said,

“Now we’re extending that idea, but rather than pointing a laser from the ground into space, we’re shining it from space, onto a telescope in space. The reason this is pertinent now is that NASA has to decide in the next couple years whether these large space telescopes will be our priority in the next few decades. That decision-making is happening now, just like the decision-making for the Hubble Space Telescope happened in the 1960s, but it didn’t launch until the 1990s.”

In order to materialize this idea of an artificial guide star, researchers checked whether a laser integrated into a CubeSat will be able to maintain the stability of a large, segmented space telescope or not. Their estimates showed that a telescope must stay perfectly still with 10 picometers for an onboard coronagraph to take an accurate measurement of a planet’s light.

Consequently, the researching team proposed a general design that would allow the laser guide star to assist the telescope and signal the onboard actuators to correct the telescope’s stability in case of a compromise. After all the experimentation and working, Douglas explained that a small fleet of guide stars should be deployed across the sky to stabilize a telescope as it explores one exoplanetary system after another.