Mooley Lab - Blog-colonizing-7nov2024

Colonizing orbital space – A threat to the night sky

It was 4th October 1957 (Moscow Time) around 10:30 pm, humans have crossed the boundary of Earth’s gravity and step into the space age with a Russian R-7 rocket carrying a 23 inches metal sphere named Sputnik. A new era started in human history. 67 years have passed and today we live in a time when launching space satellites is much easier and intricately connected to our lives. From accurate navigation systems to high-speed communications, from surveillance on enemy to exploration of new scientific adventures, everything is significantly influenced by space technology. Humans had been wondered by the beauty of cosmos from the ground and suddenly space era opens a new door. Astronomy at wavelengths which could never penetrate the Earth’s atmosphere is now opening a reservoir of knowledge about the Universe; thanks to space-based telescopes.

While leveraging the potential of near-earth space, our lives have been tremendously benefited, excessive abuse of it can create problems; which is getting unfolded slowly now. With the goal of global internet and fast communication, the ongoing and upcoming satellite mega-constellations like Starlink by SpaceX threaten the night sky. Light pollution from city lights was already a problem restricting our view of the cosmos, satellites are posing extra challenges. You go to a dark place, far from the city, you will overcome the light pollution but what can you do when the sky itself is getting polluted?

Both professional and amateur astronomy are affected. Studies have shown that the number of satellites, their leftovers, and artificial space debris are growing exponentially with time. From 2000 active satellites during 2018 has increased to ~5000 in 2020 and expected to reach over 1,00,000 during the 2030 [1].

Rapid growth of the number of anthropogenic space objects, taken from [1]

Rise in the fraction of the affected image by Zwicky Transient Facility from 2020 to 2021. Till then, only 1500 Starllink satellites were launched. See ref [2]

Satellites reflect sunlight which is visible from the ground. Nowadays, when you look up at the sky, you can very often spot fast moving illuminated objects travelling across the sky – they are the satellites. When long exposure images of the sky are taken by telescopes, these satellites leave trails, most often ruining the observations.

A long-exposure (208 min) image of Orion Nebula, taken in mid-December 2019, affected by satellite trails when the number of Starlink satellites was below 200. (Credit : A. H. Abolfath/NOIRLab/NSF/AURA)

Wide-field survey observations are most affected because long exposure and wide field of view increase the probability of having satellite trails in the images. A study at Zwicky Transient Facility with observations during twilight has shown that in late 2019, 0.5% of the total images have at least one satellite trail which increased to 18% of images during 2021 August. Also, they predicted that all the twilight observations will be damaged by the time number of deployed Starlink satellites reaches 10,000 [2]. Till September 2024, a total of ~ 6,500 Starlink satellites are launched whereas till September 2021, the total number was only 1,500. SpaceX has a plan to launch 42,000 satellites in low Earth orbit.

Satellites sometimes exhibit bright flashes of light called “glint”, which many a times mimic astrophysical transient phenomena. In 2021, a group of astronomers, while monitoring a galaxy at redshift 11 (GN-z11), noticed a 245s duration bright burst of infrared light and characterized it as a rest frame ultraviolet flash associated with a Gamma Ray Burst (GRB). While this was very unexpected, they speculated that their result may suggest that long GRBs can occur as early as 420 million years after the Big Bang which can alter our understanding of GRBs [3]. However, it was identified to be Breeze-M upper stage of a Russian Proton rocket [4].

Several such threats are posed due to overabundance of satellites. Not only professional astronomy, public stargazing, astrophotography are also severely affected. Being space enthusiasts or professional astronomers and technologists or even common public we have the responsibility to protect the night sky from anthropogenic pollution. The U.S. National Science Foundation commissioned an independent science advisory group JASON to assess the impact of current and planned large satellite constellations on astronomical observations in 2020. Based on two workshops SATCON 1 & 2, JSON reported some key recommendations in order to protect astronomical observations from the potential threats by satellite mega constellations [5].

Image taken by the Dark Energy Survey camera in 2019 (Credit:CTIO/NOIRLab/NSF/AURA/DECam DELVE Survey)

Their key recommendations include

For Observatories: Development of applications available for astronomical community to plan for observations based on satellite ephemeris to avoid satellite interference and application to identify and mask satellite trails in images during data analysis process.

For Satelllite Operators: All LEO satellites should be fainter than 7 magnitude and they should not have specular reflection in direction of observatories.

While these are significant steps to tackle the problem, they are not a proper solution. Temporarily it can bypass the issue but soon, when the number of satellites grows even more, these can never be a viable solution. As soon as possible we need to act and regulate the proliferation of satellites population in the orbital space near the Earth.

Prof. Andy Lawrence (Regius Professor of Astronomy at the University of Edinburgh) suggested considering orbital space as an environment which should be protected and preserved under the preservation rules much like forests, oceans and atmosphere. He has made several attempts (although unsuccessful) to cease SpaceX’s plan of launching 42,000 satellites by sending letters to Federal Communications Commission (body granting approval for launch of communication satellites), submitting independent court appeal regarding applicability of National Environmental Policy Act (NEPA) to space environment [6].

Prof. Lawrence with his colleagues have created an appeal [7] for professional astronomers, PhD students, technologists to spread the awareness and ask governments, institutions and agencies all around the world to provide legal protection to ground based observatories and the night sky. Another petition with is also created for common public with similar objectives [8].

It is already late, and we must act soon. Let’s all protect our night sky together.

References

[1] Lawrence, A., Rawls, M.L., Jah, M. et al. The case for space environmentalism. NatAstron 6, 428–435 (2022). https://doi.org/10.1038/s41550-022-01655-6

[2] Przemek Mróz et al 2022 Impact of the SpaceX Starlink Satellites on the Zwicky Transient Facility Survey Observations ApJL 924 L30. https://iopscience.iop.org/article/10.3847/2041-8213/ac470a

[3] Jiang, L., Wang, S., Zhang, B. et al. A possible bright ultraviolet flash from a galaxy at redshift z ≈ 11. Nat Astron 5, 262–267 (2021). https://doi.org/10.1038/s41550-020-01266-z

[4] Michałowski, M.J., Kamiński, K., Kamińska, M.K. et al. GN-z11-flash from a man-made satellite not a gamma-ray burst at redshift 11. Nat Astron 5, 995–997 (2021). https://doi.org/10.1038/s41550-021-01472-3’

[5] https://www.nsf.gov/news/special_reports/jasonreportconstellations/

[6] https://andyxlastro.me/losing-the-sky-resources/

[7] https://astronomersappeal.wordpress.com/

[8]https://secure.avaaz.org/community_petitions/en/SpaceX_and_companies_planning_to_launch_constellations_of_satellites_Losing_the_night_sky_due_to_tens_of_thousands_of_satellites/?s=03

Posted by Samrat Ghosh on Nov 7th, 2024

Samrat is a Ph.D. student working on radio VLBI studies of compact objects. He is also currently building of an astrobiology payload.