Can we secure our place in the Solar System? Not in any absolute sense because nature can be very unpredictable. But we can make the effort to safeguard our civilization by cataloguing potentially dangerous asteroids. An upcoming space telescope will help.
NASA’s SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer) mission will launch no later than April 2025. The orbiting telescope will conduct a two-year all-sky survey in optical and infrared light. The main focus of the mission is to gather data on more than 300 million galaxies and 100 million stars in the Milky Way. But SPHEREx will also add to our knowledge of Potentially Hazardous Objects (PHOs).
A new paper examines SPHEREx’s capabilities and how the mission can contribute to Planetary Defense (PD.) Its title is “Planetary Defense Use of the SPHEREx Solar System Object Catalog.” It’s currently in pre-print, and the lead author is Carey Lisse from the Space Exploration Sector at the Johns Hopkins University Applied Physics Laboratory.
SPHEREx “provides a unique space-based opportunity to detect, spectrally categorize, and catalogue
hundreds of thousands of solar system objects at NEOWISE sensitivities,” the authors write. NEOWISE is NASA’s successful asteroid-finding mission that just reached ten years of operation and has found over 3,000 NEOs (Near-Earth Objects). “By leveraging SPHEREx data, scientists and decision-makers can enhance our ability to track and characterize PHOs, ultimately contributing to the protection of our planet,” the authors of the new paper explain.
Among the many calamities that have struck life on Earth, asteroid impacts are the most dramatic. About 66 million years ago, an asteroid struck Earth and wiped out the dinosaurs. That asteroid was about 10 km in diameter and wreaked havoc on Earth’s biosphere at the time. The odds of another asteroid strike are never zero, and less massive impactors could still alter civilization forever. It could cause unimaginable suffering and strife.
While some researchers are working on ways to destroy or deflect PHOs, others are working on cataloguing as many of them as they can. This is where SPHEREx comes in.
SPHEREx will follow the same type of orbit that NEOWISE does. It’s called a sun-synchronous polar orbit, and it means that the observatory will collect data from both the leading and trailing directions. That will allow SPHEREx to cover the range of latitudes in the entire sky every six months and to cover the ecliptic poles in each orbit.
This figure from the paper shows how SPHEREx will map the sky in infrared (left.) “Utilizing a sun-synchronous NEOWISE-like polar orbit, objects in the sky at ~90 deg elongation will be observed in each great circle,” the authors explain. “The Earth’s motion around the Sun advances the great circle’s longitude ~1 deg/day, taking data in both the leading/trailing (forward/ behind) directions means that the entire sky’s range of longitudes is covered in 6 months, with the ecliptic poles observed every orbit.” The panel on the right shows the Solar System objects SPHEREx will observe, excluding the Sun, Mercury, Venus, and the innermost Near-Earth Asteroids. Image Credit: Lisse et al. 2024SPHEREx was built to address three main science goals: Measuring the Anisotropy of Cosmic Inflation,
Determining the History of Galaxy Formation, and Surveying Ices in Molecular Clouds. Detecting PHOs is its side hustle. But its powerful infrared capabilities mean it’ll do more than just detect them.
When it comes to asteroid detection, we’re in a race against time. The pace may be slow, but it’s still a race and one we can win. Time may be on our side.
PHOs are defined as objects that come with 0.05 AU of Earth and have a magnitude of 22 or less. These objects are close enough to pose an impact risk and large enough to be catastrophic if they do strike Earth. Magnitude 22 corresponds to an object with an albedo of 0.14 and a size of about 140 meters. Though much, much less massive than the dinosaur-killing Chicxulub impactor, these objects can still cause widespread damage.
Scientists predict that one of the impactors should strike Earth every few ten thousand years. As a result, Congress instructed NASA to detect 90% of these NEOs. NASA’s made lots of progress, and with the commissioning of the Legacy Survey of Space and Time, they’ll likely reach the 90% goal in less than a decade.
NASA’s “Eyes on Asteroids” site maps the known Near-Earth asteroids (NEAs) and shows the population of these objects. Some are parent bodies of meteorites found on Earth. Courtesy NASA.But SPHEREx will do more than detect PHOs, NEOs and NEAs. It will reveal crucial information that will allow us to prepare for their approach. “Accurate spectral categorization of NEOs is a key factor in assessing the threat from a potential impactor as well as developing effective mitigation strategies,” the researchers explain. “Succinctly, whether the impactor is made of rock, metal, or an icy organic mix is critical to know before one attempts to terminate the hazard (“know thy impactor”), and this determination is typically made using near-infrared spectrophotometry.”
The observatory will acquire millions of exposures of the sky, and they’ll be in 102 visual and infrared wavelengths. Some wavelengths will span the same range as NEOWISE but in 40 discrete channels rather than NEOWISE’s two channels. SPHEREx’s observations will also feature an additional 62 spectral channels beyond NEOWISE’s coverage. What does that add up to?
“SPHEREx measurements will be uniquely useful for spectral typing, quick object compositional characterization, population context, size/albedo determination, and temporal trending of objects in the
current epoch,” the authors explain. Spectral type, rotation states, albedo, and size are key factors in building up our planetary defence against asteroids and comets.
SPHEREx is an important step in safeguarding our home in the Solar System as best we can. Nature can throw a lot of powerful, vexing curveballs, and NASA’s efforts to detect them is foundational to developing ways to protect Earth.
SPHEREx will do more than find PHOs, and by characterizing them, its data could be the key to effective mitigation.
