Planetary defense: the hits keep coming


Catalina Sky Survey. Credit:

Small asteroids hit Earth’s atmosphere and explode on a regular basis – without any harm to people or property. Sometimes people see them, most times not. Various sensors systems, ranging from the network of microbarometers operated by the Comprehensive Test Ban Treaty Organization (which detect infrasound waves), lightning sensors on the National Oceanic and Atmospheric Administration’s GOES 16 and 17 weather satellites, the National Weather Service’s Next Generation Weather Radar (NEXRAD) system.

Planning for planetary defense against large asteroid impacts — events that could cause damage to people and property — requires, first and foremost, finding, tracking, and characterizing near-Earth objects (NEOs)  –(mostly) asteroids and (some) comets that are predicted to pass within about 30 million miles (50 million kilometers) of Earth on their orbits around the Sun. An expanding global network of ground-based observers is doing this work. The International Asteroid Warning Network (, now five years old, is improving communication and coordination among these observers.

I received an in-depth update on this enterprise by attending the 2019 Planetary Defense Conference (PDC), which convened in College Park, Maryland, on April 29. These biennial, week-long PDCs are an opportunity for the global community of experts involved in NEO science and planning for planetary defense to come together and report on their work. This was my third PDC. (Full disclosure: I am a consultant to NASA’s planetary defense program on communication issues. No one asked me to write this blog post.) This post provides a brief glimpse of the proceedings.

With a bigger annual budget – currently around $150 million – and the world’s first planetary defense mission – the Double Asteroid Redirection Test (DART) – in development (for launch in 2021), NASA’s planetary defense program is making progress. According to Kelly Fast, manager of NASA’s NEO observations program (a key element of the planetary defense program), the ongoing NEO survey hit the 20,000 mark on April 26. That is, observers (more than 90 percent funded by NASA) have found more than 20,000 NEOs thus far. NEO discoveries reached 15,000 in October 2016, a milestone marking a 50 percent increase in discoveries since 2013, when the 10,000 threshold was reached. In 2012 the rate of NEO discovery was about half of what it is today. (As of June 2, discoveries totaled 20,224).

Two space agencies now have planetary defense officers: Lindley Johnson at NASA, and Ruediger Jehn at the European Space Agency (ESA). Planetary defense could involve launching a mission to deflect an asteroid off an impact course with Earth (the DART mission will demonstrate this technique on a non-hazardous asteroid), or, if deflection is not an option, planning for impact mitigation. No known NEO is predicted to be on an impact course with Earth for the next 100 years. Observers have found, and are tracking, most of the big ones – 1 kilometer in size or larger – objects that might cause global damage if they were to impact Earth (either by exploding in the atmosphere or hitting land or sea).

Though the network of NEO observation sites has been growing in recent years and while NEO observing technologies and techniques are improving, ground-based observations can only be conducted at night when skies are clear. These limitations mean that using current assets, says NASA’s Lindley Johnson, it would take 30 years to meet the congressionally mandated goal of finding, tracking, and characterizing 90 percent of 140-meter and larger NEOs (Congress wanted this goal met by 2030).

Given these limitations, the planetary defense community has been advocating for a space-based NEO survey telescope that will observe in the infrared (IR). NASA’s planetary defense program is funding an “extended-phase-A” study of the proposed NEO Camera (or NEOCam) mission – a space-based, dedicated NEO survey telescope. The primary challenge is to refine key technology for the mission — and then, if all goes well, advance to “phase B” — mission definition.

As NEOCam principal investigator Amy Mainzer explains, asteroids typically reflect less than 10 percent of the sunlight that hits them in visible wavelengths. This visible light reflection is what ground-based observers can detect. The rest of the sunlight that hits an asteroid is emitted in infrared (IR wavelengths – hence, the desirability of an IR NEO survey telescope.

Meanwhile, the NASA-funded Catalina Sky Survey and the Pan-STARRS project are the two most productive NEO search initiatives. A newer asset, funded by NASA in 2013, is the Asteroid Terrestrial Impact Last Alert System (ATLAS), which aims to provide one day’s warning for an impact of an asteroid that would release 30 kilotons of energy, one week for a 5-megaton impact event, and three weeks for a 100-megaton impact event. The privately funded Las Cumbres Observatory, a global network of robotically operated telescopes, devotes some of its observing time to NEO searching.

The DART mission, being the first of its kind, presents numerous technical challenges. For instance, according to Angela Stickle, a member of the DART team at the Johns Hopkins Applied Physics Laboratory (APL), which is building the spacecraft, “initial impactor parameters” – such as impactor mass and speed – “are well known.” However, “physical properties of the target are not well known.” Factors that could affect the kinetic impact demonstration include the porosity, strength, and crack spacing of the asteroid target.

Finally, I’d like to say a few words about a first-time event for a PDC – a panel of journalists (organized by yours truly) who were invited to PDC 2019 to tell the experts what they need to know about planetary defense and how and when they need to know it.

Journalists on the panel were science reporter Dan Vergano with Buzzfeed News, science reporter Sarah Kaplan with the Washington Post, and broadcast meteorologist Melissa Nord of CBS Channel 9 TV in Washington, D.C. (Broadcast meteorologists routinely report on natural phenomena such as asteroid close approaches and meteor showers.)

Addressing ongoing concerns among some scientists about erroneous reporting, Kaplan told attendees, “You need to know how hard we work to get it right.” She said she would much rather be corrected during interviews than have to correct a story after publication. Kaplan said people in the planetary defense community use too much technical jargon in communications with journalists. Don’t “dumb it down” for us, she said. Instead, “translate” – that is, take the time to explain what you are telling us about.

All three panelists said the planetary defense community needs to put more thought into graphics provided to journalists and the public. Graphics that are useful and meaningful to experts are not necessarily useful, meaningful, or comprehensible to others. All three also expressed frustration at having to go through public affairs offices in order to make contact with experts. They prefer communicating directly with sources. With deadlines always looming, having to wait for hours to get in contact with an expert can mean that a story is published or aired without comment from the appropriate person. “It’s tremendously frustrating,” Vergano said; “the PR folks often get in the way.”

Vergano urged experts not to “fudge” on what they do not know for sure. We can live with uncertainty, he said. And we need patience from our sources, he added.  He also advised experts to “get over” their frustrations with headlines and stories that might appear misleading or sensationalized to them. Journalists are not going to use the same scientific language that the experts use, he said.

Nord, who serves a local audience but in a large metropolitan area with an educated population, suggested that NASA’s PDCO could better assist broadcast meteorologists working in smaller towns by providing them a short video on NEOs, close approaches, and planetary defense. (Good idea.)

That’s all for now.

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