It has been an eventful week for astronomers around the world. On 17 April, five asteroids, ranging from the size of a car to that of an aeroplane, flew past Earth. The asteroid with the closest approach was 2023 HB, around 2.9m in size; it whizzed past our planet at a distance of approximately 195,000km, based on data from the US space agency Nasa JPL (Jet Propulsion Laboratory) asteroid watch dashboard.
The good thing is: You don’t have to worry about an asteroid threat. Not for the time being at least. One thing that is hard to miss, however, is the growing curiosity—and awareness—about asteroids and other near-Earth objects, or NEOs, like comets. News alerts on “a terror rock” or a “potentially hazardous” space rock hurtling towards Earth are now commonplace.
Astronomers usually follow two methods to detect asteroids. The first is all-sky surveys, which map the night sky with no particular observational target in mind. The Catalina Sky Survey (CSS), a Nasa-funded project, is a famous example of a sky survey working towards the discovery of asteroids and comets. Founded in 1998, CSS—based at the University of Arizona’s Lunar and Planetary Lab in Tucson—has discovered more NEOs than any other survey in the world.
Sometimes, though, asteroids can be too faint to spot in an all-sky survey. That is where the second method comes in: large telescopes. These strong telescopes have a smaller field of view—they will only see a small, specific part of the sky—but can observe objects in much more detail, gathering terabytes of data.
Even with all the high-tech equipment and large amounts of funding, however, it’s difficult for astronomers and space agencies to keep an eye on every moving object in space. Pitching in, almost like a third potent tool, are amateur and semi-professional astronomers, citizen scientists from across the world. Armed with software tools and a passion for astronomy, these “asteroid hunters”—ranging from schoolchildren to retired professionals for whom astronomy is not a full-time profession—form a big network of celestial police that is playing a key role in the discovery of NEOs.
After initial training, amateur astronomers and asteroid hunters rely largely on astronomical data sets and images shared by large sky surveys to spot these objects. In some instances, amateur astronomers have even spotted celestial objects from archival photographs of the night sky. Some, of course, do contribute to asteroid research with the help of telescopes too, though these can be expensive. Recently, amateur skywatchers published a study, in the Nature journal, that describes how the asteroid Dimorphos became temporarily brighter and redder when Nasa’s Double Asteroid Redirection Test (DART) spacecraft hit it. Nasa describes DART as the first mission to investigate and demonstrate a method of asteroid deflection by changing an asteroid’s motion in space through kinetic impact.
The skywatchers who published this paper were able to make their observations using a type of smart digital telescope—made by the France-based company Unistellar—which is becoming increasingly popular among amateur skywatchers in the West. It’s easy to use, can be activated remotely and enables them to connect in real time to professional scientists
In fact, in 2022, citizen astronomers with the Unistellar Network, a worldwide citizen science community, submitted 542 reports on 32 different asteroids to the Minor Planet Center (MPC), the official repository for data on NEOs. Founded in 1947, this international organisation comes under the ambit of the International Astronomical Union (IAU) and operates at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, US.
There are similar communities and asteroid search campaigns in India too. “Amateur astronomers and students are very involved in projects that look for asteroids. The most popular of these projects is run by the (citizen science programme) IASC (International Astronomical Search Collaboration)…. IASC collaborates with the Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) Observatory in Hawaii to scan and take images of the sky which are then provided to participants as educational outreach,” says Delhi-based Mila Mitra, co-founder and academic head, STEM and Space, an education initiative and startup set up in 2019 to promote interest in STEM (science, technology, engineering and mathematics).
As an astrophysicist, Mitra has worked for more than 20 years at Nasa’s Goddard Space Flight Center and Nasa Ames Research Center, both key research bodies for the US space agency, on satellite missions. She has also been the country coordinator for programmes such as Asteroid Day and Global Astronomy Month in India.
According to the IASC website, people interested in these search campaigns should join as a team with at least two members. The IASC can help you form a group by connecting you with other participants in your area. All you need thereafter is access to a Windows computer and an internet connection.
Apart from the IASC, the virtual network Zooniverse, a popular citizen science portal started in 2009, conducts similar campaigns around the world with organisations such as the European Space Agency (ESA) and Nasa.
Amateur astronomers, including students, analyse the data from these surveys and large telescopes through a software called Astrometrica and try to identify asteroids, Mitra explains on email. “This programme (from the IASC) is hugely popular in India. It has been running for more than 10 years and students from all over India have participated. Citizen scientists enjoy looking through real images and treat it almost as a computer game. It also gives participants a chance to access real scientific data from observatories,” she adds. STEM and Space has also trained and involved more than 2,000 students in this programme over the last three years. It has led to 75 provisional (or confirmed) asteroid discoveries.
It’s quite possible that an asteroid spotted by a school student might already have been discovered. But, as Mitra explains, when this data is constantly analysed, scientists are able to map the orbit of these objects better. This, in turn, helps them track the asteroid more carefully.
Participation in such campaigns is just the first step in a long process to spot these space rocks. The data sets shared with citizen astronomers are essentially stationary astronomical images that contain all sorts of objects—stars, galaxies, quasars, even space debris. These images—which come in a format called FITS, or Flexible Image Transport System, the most commonly used digital file format in astronomy—can only be opened and analysed in specialised software like Astrometrica or SAOImageDS9.
The software opens these images in a moving sequence, creating a loop of sorts, almost like a flipbook. “In these data sets, you have to look for celestial objects that are moving in a straight line. There are three-four more parameters. It could be a planet, an asteroid or a comet. You have to look very carefully,” says Aryan Mishra. The 23-year-old is a self-taught astronomer and founder of the Delhi-based startup AstroScape.
In his relatively young career so far, Mishra has observed close to 500 NEOs. But only one of them was considered an asteroid discovery, in 2014, and designated the number 2014–00372. Mishra says a big reason for the growing interest in asteroids is simply because “they are very near to us”. “If I talk about discovering a black hole, that is something that takes years. To find a black hole, you need to keep observing that specific part of the universe for a decade at least. But these asteroids are orbiting the sun. They pass by Earth frequently,” adds Mishra.
Like any scientific process, asteroid search campaigns take time—they can easily run for 30 days or more. Citizen astronomers also have to be mindful and accurate while recording the measurements (the time and position of an object as it moves from point X to point Y) and identifying true and false signatures since not all moving things are asteroids; for example, observing whether or not the object is moving along a straight line and at a constant speed.
These recorded observation reports are then sent to the MPC and IAU for evaluation. If these preliminary, or valid, detections meet the set criteria, they become “provisional” (or verified) in status and are “numbered” at the final stage.
Sometimes, spotting an asteroid can come down to sheer luck, says Joshi Yogeshkumar Dileepkumar, a master teacher with the IASC. The 25-year-old engineer works with the department of science and technology (DST), Rajasthan, and organises the DST-Rajasthan Asteroid Search Campaign, started in April 2020 during the initial covid-19 lockdown in India. Its most recent edition started on 17 April and will run till 12 May. “The craze around space has increased a lot in the last few years. Isro (India’s space agency) has had so much success in the recent past with the Mangalyaan and Chandrayaan missions. You could also say it’s the movies (themed on space). All this has rubbed off on the general public, including students, in a good way. That’s why people are looking for opportunities to contribute to space activities,” adds Joshi, who has made more than 100 preliminary asteroid detections so far. None of them, though, has been given provisional status.
Joshi explains that students and amateur astronomers have very small telescopes with primary mirrors in inches that cannot spot asteroids easily. “Even if someone wants to buy a telescope with a 1m mirror, it’s too expensive (for instance, telescopes from Unistellar, start from $2,499, approximately ₹2 lakh). That’s why the chances of amateur astronomers spotting an asteroid with their own telescopes are quite less. On top of that, there’s so much pollution in our country. You need clear night skies to even have a chance of spotting something,” adds Joshi.
Despite such hurdles, school students across India have shown considerable interest in asteroid search campaigns in recent years. Many recent provisional discoveries have been recorded by students from Gujarat and Maharashtra, according to recent news reports. Rajasthan has also come in for mention.
Divyendu Sen, a biology lecturer at the Government Senior Secondary School at Unhel in Rajasthan’s Jhalawar district, has been participating in asteroid search campaigns since 2020, along with his students. Sen, 36, learnt about the campaigns through DST and trained his students on the intricacies of spotting asteroids after researching on Nasa and the IASC through YouTube videos.
Together, Sen and his students have made 10 provisional asteroid discoveries, with more than 50 students from the school, from classes IV-XII, participating in asteroid search campaigns over the last three years. Their last provisional discovery was in 2022, he says on the phone. “I think the big motivation for them is that a student from such a small village can have an asteroid under their name. A lot of the students want to name the asteroids after our school but we have suggested that they name it after the likes of (astronauts) Rakesh Sharma and Kalpana Chawla,” says Sen.
According to data from the MPC, 690 near-Earth asteroids have been discovered so far this year; 83 have been found in April alone. While that number is sure to increase, the discovery of the first asteroid goes back more than 200 years. On 1 January 1801, Italian mathematician and astronomer Giuseppe Piazzi, at the Palermo Astronomical Observatory in Sicily, discovered Ceres, which is today classified as a dwarf planet, while working on a catalogue of star positions. According to archival information from the Nasa JPL, Piazzi used a telescope instrument called the Ramsden Circle to discover the object whose “light was a little faint and colored as Jupiter”.
While looking at it again on subsequent nights, Piazzi saw that its position changed slightly. Piazzi presented his discovery to other astronomers initially as a comet or a star but did not reveal the data from his observations, leaving other astronomers puzzled about the object’s true nature. Interestingly, it was around this time that a group of German astronomers established a society called the “celestial police” to find Piazzi’s object, which, they believed, was a missing planet.
The methods and technology used to find asteroids and other NEOs have come a long way since. “The observing techniques have changed over centuries,” says Peter Veres, an astronomer at the Harvard & Smithsonian Center for Astrophysics and the Minor Planet Center. “First asteroids (early 19th century) were discovered visually through a telescope. Late in the 19th century, the photographic plates significantly increased the number of discoveries. The next step up was the introduction of CCD (charged-coupled device) cameras late in the 20th century. But the method is generally the same: blinking and comparing images of the same area of the sky while the stars are tracked (static) but the asteroid or a comet moves,” Veres says on email.
Synthetic tracking is one of the more recent techniques where near-Earth asteroids are spotted with the help of multiple short-exposure images to observe moving objects. This method is only possible through fast computers and parallel processing allowed by graphics processing units. Veres says synthetic tracking allows smaller telescopes, which cost less than larger ones, to deliver good results.
Astronomers have also turned to Machine Learning and Artificial Intelligence (AI). In May last year, for instance, an international group of astronomers announced that they had found 1,701 new asteroid trails in archival data from the Hubble Space Telescope—as part of the Hubble Asteroid Hunter project, which combined the efforts of an AI model and more than 11,000 citizen scientists.
Could the introduction of AI and Machine Learning in the process of spotting asteroids diminish the role of amateur astronomers?
“Machine Learning will always need to be backed up by human involvement and intervention,” says Somak Raychaudhury, vice-chancellor, Ashoka University, who was previously the director of the Inter-University Centre for Astronomy and Astrophysics (IUCAA) in Pune, Maharashtra.
Raychaudhury believes the role of amateur astronomers in all categories, be it spotting black holes or asteroids, is important. “Because there are far more amateur astronomers in the world than there are professional astronomers,” he adds, citing examples of the International Liquid Mirror Telescope (in Devasthal, Nainital, Uttarakhand) and the Rubin Telescope in Chile and explaining why there is a need for more people to keep an eye on the night sky. These two recently set up observatories are expected to release a huge amount of data and images, which will eventually come into the public domain and require assistance from citizen astronomers. “The citizen science angle in ‘asteroid watch’ is becoming a big thing,” says Raychaudhury.
While planetary defence is one aspect of asteroid discoveries that is constantly evolving, there are also recent examples of extraordinary asteroid missions, centred on asteroid mining and astrobiology, that are helping the world look beyond the destructive angle of these space rocks. The most exciting of the lot is the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer)—Nasa’s asteroid-study and sample-return mission, launched in 2016.
After reaching the near-Earth asteroid Bennu in December 2018 and matching its speed and orbit, the van-sized spacecraft successfully touched down on the asteroid on 20 October 2020, scooping up a sample—weighing roughly 60g—from the rock’s surface. The spacecraft is slated to return to Earth later this year with the sample, which is expected to help scientists learn more about the formation of our solar system.
It was, in fact, a citizen science project focused on asteroid Bennu that inspired Delhi-based Sovan Acharya, 55, to start hunting for asteroids. Started in 2019 by Nasa, in partnership with CosmoQuest, a project run by the US-based Planetary Science Institute that supports citizen science initiatives, this project invited citizen scientists to help measure Bennu’s boulders, map its rocks and craters, and choose the sample collection site on the asteroid.
After participating in this 2019 project, Acharya, a former civil engineer, started the SA Citizen Science Group in 2020 and has been participating in asteroid search campaigns ever since. Today, his group has around 270-280 members around the world—everyone from young students to former Isro scientists.
He has made more than 100 preliminary asteroid detections; his group has made seven provisional discoveries. The provisional asteroid 2021 PT33 is one such example. “I have been a civil engineer for more than 30 years of my life and I always worked with sand and rocks. Reading science books was a particular source of joy for me. I then told myself that I should do something with the space community as well,” Acharya says on the phone.
He intends to build on his passion for discovering celestial objects—having already contributed to projects that explore supernovas and exoplanet candidates. “There is a lot of scope in engaging with science. Even at the school level, science communities and clubs should include citizen science projects. All they need is a laptop and they can connect with scientists across the world.”
An editorial published in Nature earlier this month, on the Nasa DART mission and how astronomy continues to benefit from working scientists collaborating with amateur colleagues, adds to what Acharya says. “As science becomes ever-more specialized and dependent on ever-more-specific instrumentation, it is tempting to think that the day of the amateur scientist is over. But this would be wrong.... The next time you’re looking for an observation partner or someone to help crunch data, consider the amateur.”