Ed Lu wants to save Earth from killer asteroids.
Or at least, if there is a large space rock that opens our way, Dr. Lu, a former NASA astronaut with a doctorate in applied physics, wants to find him before he reaches us, hopefully with years of prior notice and an opportunity for humanity. to divert it.
On Tuesday, the B612 Foundation, a non-profit group that Dr. Lu helped found, announced the discovery of more than 100 asteroids. (The name of the foundation is a look at Antoine de Saint-Exupéry’s children’s book, “The Little Prince”; B612 is the main character’s domestic asteroid.)
This in itself is not remarkable. Sky observers around the world are constantly reporting on new asteroids. This includes fans with backyard telescopes and robotic surveys that systematically scan the night sky.
What is remarkable is that B612 did not build a new telescope or even make new observations with existing telescopes. Instead, B612-funded researchers applied cutting-edge computing power to ancient images, 412,000 of them in the digital archives of the National Optical-Infrared Astronomy Research Laboratory, or NOIRLab, to filter asteroids from 68 billion cosmic light points. . captured in images.
“This is the modern way of doing astronomy,” said Dr. Lu.
The research adds to the “planetary defense” efforts of NASA and other organizations around the world.
Today, of the estimated 25,000 asteroids close to Earth, at least 460 feet in diameter, only about 40% have been found. The other 60 percent, about 15,000 space rocks, each with the potential to release energy equivalent to hundreds of millions of tons of TNT in a collision with Earth, has not been detected.
B612 collaborated with Joachim Moeyens, a graduate student at the University of Washington, and his doctoral advisor, Mario Juric, a professor of astronomy. They and their colleagues at the university’s Intensive Data Research Institute in Astrophysics and Cosmology developed an algorithm that is capable of examining astronomical images not only to identify those points of light that could be asteroids, but also to find out what points of light in the pictures taken. Different nights are actually the same asteroid.
In essence, researchers have developed a way to discover what has already been seen but not realized.
Asteroids are usually discovered when the same part of the sky is photographed several times overnight. A strip of the night sky contains a multitude of points of light. Far stars and galaxies remain in the same arrangement. But objects that are much closer, within the solar system, move quickly and their positions change overnight.
Astronomers call a tracklet a series of observations of a single moving object overnight. A tracklet provides an indication of the movement of the object, telling astronomers where to look for it another night. They can also search for old images for the same object.
Many astronomical observations that are not part of systematic asteroid searches inevitably record asteroids, but only at one time and place, not the multiple observations needed to put the tracklets together.
NOIRLab images, for example, were taken primarily by Chile’s 4-meter Victor M. Blanco Telescope as part of a survey of nearly one-eighth of the night sky to map the distribution of galaxies in the universe.
Additional points of light were ignored because they were not what astronomers were studying. “It’s just random data in random images of the sky,” said Dr. Lu.
But for Mr. Moeyens and Dr. Juricus, a single point of light other than a star or galaxy is a starting point for its algorithm, which they called Heliocentric Orbit Recovery without Tracklet, or THOR.
The motion of an asteroid is precisely dictated by the law of gravity. THOR constructs a test orbit that corresponds to the observed point of light, assuming a certain distance and speed. Then calculate where the asteroid would be on the following and previous nights. If a point of light appears in the data, it could be the asteroid itself. If the algorithm can link five or six observations over a few weeks, this is a promising candidate for asteroid discovery.
In principle, there are an infinite number of possible test orbits to examine, but this would require an impractical eternity to calculate. In practice, because asteroids are grouped around certain orbits, the algorithm only has to consider a few thousand carefully chosen possibilities.
However, calculating thousands of test orbits for thousands of potential asteroids is a huge task for calculating numbers. But the advent of cloud computing, a great computing power and data storage distributed over the Internet, makes it feasible. Google contributed time to its Google Cloud platform to the effort.
“It’s one of the most interesting applications I’ve ever seen,” said Scott Penberthy, Google’s director of applied artificial intelligence.
To date, scientists have examined approximately one-eighth of the data for a single month, September 2013, in the NOIRLab archives. THOR produced 1,354 possible asteroids. Many of them were already in the asteroid catalog maintained by the Minor Planet Center of the International Astronomical Union. Some of them had been observed before, but only for one night and the tracklet was not enough to safely determine an orbit.
The Minor Planet Center has confirmed 104 objects as new discoveries so far. The NOIRLab archive contains seven years of data suggesting that there are tens of thousands of asteroids waiting to be found.
“I think it’s fantastic,” said Matthew Payne, director of the Minor Planet Center, which was not involved in the development of THOR. “I think it’s very interesting and it also allows us to make good use of the archive data that already exists.”
Currently, the algorithm is configured to find only asteroids in the main belt, those with orbits between Mars and Jupiter, and not asteroids close to Earth, which could collide with our planet. Identifying asteroids close to Earth is more difficult because they move faster. The different observations of the same asteroid can be separated further in time and distance, and the algorithm must make more numbers of numbers to make the connections.
“It will definitely work,” Mr. Moeyens. “There’s no reason why I can’t. I haven’t really had a chance to try it.”
THOR not only has the ability to discover new asteroids in old data, but it could also transform future observations. Take, for example, the Vera C. Rubin Observatory, formerly known as the Large Synoptic Survey Telescope, currently under construction in Chile.
Funded by the National Science Foundation, the Rubin Observatory is an 8.4-meter telescope that will repeatedly scan the night sky to keep track of what changes over time.
Part of the observatory’s mission is to study the large-scale structure of the universe and detect exploding distant stars, also known as supernovae. Closer to home, you will also see a multitude of bodies smaller than a planet whistling around the solar system.
A few years ago, some scientists suggested that the observation patterns of the Rubin Telescope could be adjusted so that it could identify more asteroid tracks and therefore locate more dangerous, as yet undiscovered asteroids more quickly. But this change would have slowed down other astronomical research.
If the THOR algorithm proves to work well with Rubin’s data, then the telescope should not scan the same part of the sky twice a night, which would allow it to cover twice the area.
“This, in principle, could be revolutionary, or at least very important,” said Zeljko Ivezic, director of the telescope and author of a scientific paper describing THOR and testing it with observations.
If the telescope could return to the same point in the sky every two nights instead of four, this could benefit other research, including the search for supernovae.
“That would be another impact of the algorithm that doesn’t even have to do with asteroids,” Dr. Ivezic said. “This is showing very well how the landscape is changing. The science ecosystem is changing because now software can do things that 20, 30 years ago you wouldn’t even dream of, you wouldn’t even think about.”
For Dr. Lu, THOR offers a different way to achieve the same goals you had a decade ago.
At the time, B612 was looking at an ambitious and much more expensive project. The nonprofit was going to build, launch, and operate its own space telescope called the Sentinel.
At that time, Dr. Lu and the other B612 leaders were frustrated by the slow pace of the search for dangerous space rocks. In 2005, Congress passed a mandate for NASA to locate and track 90 percent of asteroids close to Earth with diameters of 460 feet or more by 2020. But lawmakers never provided the money that NASA needed to carry out the task, and the deadline passed with less than half of these asteroids found.
Raising $ 450 million from private donors to subscribe to the Sentinel was difficult for the B612, especially since NASA was considering its own space telescope to find asteroids.
When the National Science Foundation approved the construction of the Rubin Observatory, B612 re-evaluated its plans. “We could turn around quickly and say,‘ What’s a different approach to solving the problem we have to solve? ’” Dr. Lu.
The Rubin Observatory will make its first test observations in a year’s time and will be up and running in about two years. Ten years of Rubin’s observations, along with other asteroid research, could finally reach the 90 percent goal of Congress, Dr. Ivezic said.
NASA is also stepping up its planetary defense efforts. Its asteroid telescope, called the NEO Surveyor, is in the preliminary design phase, with the aim of launching it in 2026.
And later this year, its double …