Arushi Nath.

The 8th Planetary Defense Conference was held at the United Nations Office for Outer Space Affairs (UNOOSA) in Vienna, Austria, from 3 - 7 April 2023. 

The Conference, organized by the International Academy of Astronautics, is held once every two years and brings together engineers, experts, and policymakers from space agencies, universities, and government ministries around the world to discuss the threat of asteroids, how to deflect them and share their strategies on planetary defense.

I was thrilled that my research abstract, "Citizen Science for NASA DART Mission: How I Used Robotic Telescopes, Open-Data, Python, and Maths to Study the Didymos System Before and After the Impact," was accepted as an in-person poster presentation at the Conference. Two years I gave an oral presentation of research on asteroid Apophis (Aiming for Asteroid Apophis) via webcam as the 2021  Planetary Defense Conference was held virtually.

The poster presentation session was held on April 4th at the rotunda of the UNOOSA. There were over 80 posters presented, and hundreds of participants attended the presentations.

It was an "out of this world" experience to present my research on determining the physical properties of near-earth asteroids and measuring the success of the NASA Double Asteroid Redirection Test (DART) mission to attendees from NASA, European Space Agencies, United Nations, Government Ministries and other researchers and students.  Why?

For two reasons:
1. I had spent over 800 hours in the past year working on the project I was presenting, and it was the most complex project I had taken and completed so far!
2. It was bizarre that I was getting to present my project to the NASA DART team, several of whom I had seen on the live television broadcast when NASA successfully impacted the asteroid Dimorphos on 26 September 2022. Some of these team members I had corresponded over emails and Twitter and was finally able to meet them in person. 

You can check out the pdf version of my poster presented at the 2023 Planetary Defense Conference. You can also view an interactive version of my poster.

I presented my poster to over 50 people individually and in groups. There were lots of interesting questions, feedback and encouragement I received. Many participants asked me to explain the methodology I had followed for generating rotation period and mutual orbital period light curves before and after the DART Impact. It was reassuring to realize that everyone found the methodology robust and were impressed by the fact that it used only middle to high-school maths to produce accurate results.

Some questions were related to the technical aspects of the algorithm I had developed, namely the computing language and the libraries I used for determining the physical properties of the asteroids. Of course,  the answer was an easy one: Python and its libraries (Matplotlib, NumPy, AstroPy)

Others were keen to know how I got access to the robotic telescopes, and the observation plans I created for gathering data on the Didymos system.  I was able to show them the research proposals I had prepared for various observatories to get observation time and share common elements of all my observation plans, namely exposure time, observation period, transit time, air mass and moon illumination to get a signal-to-noise ratio of over 100 for my observations.

Some of the most interesting questions were about how I got started, who was my mentor, how I planned to take the project further, and what are my future career plans. 

I was able to share insights into the collaborations I forged at different stages of the project, forums I turned to seek answers to problems I faced,  and online Zoom conferences I participated in to build up knowledge about asteroid photometry. 

I was able to answer all the questions confidently, as I knew all aspects of my project in detail. The conversations were educational, friendly and fun. I had a realization that I  actually enjoyed answering questions as so many participants had taken time out to listen to me and understand my project. I am grateful to all those who turned up for my poster presentation.

I had an opportunity to check the poster of other presenters and ask them questions.  It was amazing to be surrounded by so many posters on almost every aspect of asteroid research and those related to past, ongoing and new space missions to the asteroids.

I enjoyed the poster presented by Tim Lister, Nahum Melamed and Dr. Helen Usher.

Tim Lister: DART Time of Impact Observations and Long-Term Photometry of Didymos from the LCOGT Network

Nahum Melamed: Applying Centrifugal Propulsion to Enable Asteroid Deflection

Helen Usher: Using Killer Asteroids to Engage Children in Astronomy and Science 'Helping NASA Save the Planet'

Other posters I found to be of interest were about: Characterisation of Impact Ejecta, Changes in Apophis Rotation and Surface Gravity During its 2029 Earth Flyby, Near Earth Object Modelling and Payloads for Protection (NEO-MAPP) project, and Observations of the DART Impact from Chile and Kenya. It was very fascinating to see that JWST was also being used to study the Didymos binary system. JWST Observations of the Didymos-Dimorphos System (poster by Dr. Cristina Thomas).

The five-day conference included a wide range of talks, presentations, and panel discussions covering different topics related to planetary defense, including the latest developments in asteroid detection, characterization, and deflection.

Each day featured two to three sessions, with around 15 presentations from different people, each lasting 10 minutes.

My favourite session was the DART Mission and LICIACube, where experts from NASA and the European Space Agency discussed the kinetic impactor mission, its impact, the pictures taken during and after impact, and the post-impact analysis. The momentum transfer efficiency was double that of predicted due to the high volume of ejecta coming out of Dimorphos. I learned how they made shape models of Dimorphos and how it became more accurate after impact since LICIACube got to view all sides of the asteroid. It was great to listen to the experts talk on the subject after spending a year creating my own algorithms to measure the changes after the impact.

Even if we had not much prior knowledge on Dimorphos, considerable knowledge about Didymos had been acquired through ground-based light curve observations dating back to 2003. Spectroscopic analyses revealed a composition typical of asteroids found within our solar system, similar to Chelyabink and Ikotawa of Hayabusa. The asteroid impact occurred with remarkable accuracy, a mere 2 meters from the intended target. Researchers closely monitored the evolution of ejecta using both ground and space telescopes, noting that initially, the ejecta moved in the opposite direction of the incoming spacecraft (first row, first few hours), later forming a captivating tail as the material was swept back. It is astonishing that a mere 160-meter object could produce approximately 10 million kilograms of ejecta.

During the post-impact phase, mutual events played a crucial role in measuring various parameters. Observations of occultations and eclipses allowed for the detection of a decrease in brightness, aiding in determining changes in the orbital period. For orbit determination prior to impact, the first and last images were utilized, obtaining 16 observations over a span of one and a half minutes. These observations proved effective in measuring the separation between the centers of mass of the two objects. Approximately 12 hours after impact, the first Goldstone detections and confirmations were obtained through the transit of radio waves. Echo reflections were received 1.30 minutes after being sent, with a broader echo originating from Didymos and a narrower spike from Dimorphos. The best-fit parameters were calculated, albeit with some uncertainty, including period change and a velocity change of 2.7 mm/sec. Notably, the post-impact phase exhibited an eccentricity of 0.025, contrasting the circular pre-impact orbit.

To calculate momentum transfer accurately, knowledge of the mass is essential, which, unfortunately, was not directly measured by DART. In order to address this, the mass was parameterized based on the density of Dimorphos, and the estimated momentum transfer was found to be enhanced within a range of 2.2 to 4.9, depending on the mass of Dimorphos. This enhancement occurred due to the recoil resulting from the ejecta. Assuming that Dimorphos and Didymos share the same density of 2400 kg per cubic meter, the calculated momentum transfer amounts to approximately 3.61.

In conclusion, the momentum transfer was more than double the initial value, resulting in a greater amount of deflection. This has significant implications for planetary defense, as it implies that we can deflect larger asteroids with the same warning time or require less warning time for asteroids of the same size.

The Italian Space Agency’s LICIACube contributed valuable information regarding the DART mission. Three minutes after the impact, the closest approach to Dimorphos was achieved. Geological and morphological analyses were conducted, focusing on determining the volume, shape, and composition information through color assessments. During one of the closest approaches, an ejecta cone was observed, indicating that the surface of Dimorphos was entirely covered by the plumes resulting from the impact. Ongoing research involves studying the plumes to determine their velocity and direction, as well as investigating color variations to understand their potential relationship with surface and subsurface materials. These efforts aim to gain a deeper understanding of the asteroid's characteristics and composition.

The Hera mission, part of the AIDA (Asteroid Impact and Deflection Assessment) framework for planetary defense, successfully imaged the ejecta resulting from the DART impact. Its main goal is to understand why Dimorphos reacted in the way it did to the impact. While only one face of the asteroid system could be observed, efforts were made to obtain images of the back side for better shape modelling. Having multiple perspectives would aid in understanding the binary formation and estimating the mass more accurately.

Accurate determination of the parameter beta, crucial for understanding the dynamics of binary asteroids, requires precise measurements of mass and semi-major axis. However, important questions remain regarding the internal structure of Dimorphos. Is it an aggregate with boulders and aggregates, and does it possess an unknown core? Is the core covered with gravel and boulders on the outside? To validate the outcomes of the DART impact and binary formation, it is crucial to ascertain the correct internal properties.

To address these uncertainties, direct measurements are necessary. The final outcome of the Hera mission will provide insights into the existence of a crater and the altered appearance of Dimorphos post-impact. These findings will refine models and reduce the number of free parameters, ultimately enhancing our understanding of asteroids and informing future planetary defense strategies.

Hera is the European contribution to an international AIDA (Asteroid Impact Deflection Assessment) cooperation. It will provide a detailed post-impact survey after the NASA DART mission. The planetary defense objectives of the Hera mission are to measure the mass of Dimorphos to determine precisely the momentum transfer efficiency, investigate the crater in detail to improve our understanding of the cratering process in the low-gravity regime and the mechanisms by which the crater formation is related to the momentum transfer efficiency.

The spacecraft would do Mars Flyby and some deep space manoeuvres to reach asteroid Dimorphos. The spacecraft includes two CubeSats, Milani and Juventas. In addition, the mission payload includes asteroid framing cameras (for science and navigation), an altimeter (for measuring the distance to the asteroid and shape modelling), a thermal infrared imager (for getting spectral information), a radio science experiment (to measure the gravity field of Didymos system) and Hera platform would serve as a baseline for other space missions including comet interceptors, and the European Space Agency’s Rapid Asteroid Mission for SEcurity and Safety (RAMSES) mission to near-earth asteroid Apophis.

Brent Barbee, Flight Dynamics Engineer at NASA's Goddard Space Flight Center in Maryland: Asteroid Deflection

The "Mission Options Analysis" is done by a large cross-agency team consisting of NASA, JPL, National Laboratories, and NASA AMES. The proposed missions would be a mix of "Flyby Missions" to reduce uncertainties in the physical properties of asteroids and "Rendezvous Missions" that would orbit with the asteroid. They would provide detailed information and eliminate uncertainties related to the impact location on Earth. Confidence in the size of the asteroid would determine its mass. 

Asteroid impactors could be kinetic or nuclear. Kinetic impactors are more useful if we have over 5 years of warning. The number of launches increases with the size of the asteroid. Multiple kinetic impactors may be needed to deflect a large asteroid sufficiently to miss the Earth. In case of a lesser warning period and large asteroid size, the nuclear option may be the only choice for complete deflection. 

We could even opt for partial deflection, like deflection to the oceans, to avoid using nuclear weapons. But tsunamis and other climate effects could happen with ocean impact, especially for larger asteroids.

An important thing to consider is that the launch times of these missions cannot change as they are fixed by orbital dynamics.

Kelly Fast, Program Scientist in the Planetary Science Division at NASA Headquarters: Introduction to IAWN and SMPAG

IAWN fits into the recommended structure of the UN to determine the impact time and severity of an asteroid determined to be on a collision course with Earth and works together with the Space Mission Planning Advisory Group (SMPAG). While IAWN is organized by NASA, SMPAG brings together all space agencies and is chaired by the European Space Agency. The United Nations Office for Outer Space Affairs (UNOOSA) serves as the permanent secretariat to SMPAG.

The IAWN notification threshold is 1%, decided by SMPAG. IAWN will notify the chair of SMPAG and UNOOSA of predicted impacts exceeding a probability of 1% for all objects characterized to be greater than 10 meters in size.

The information will be rolled out as follow:
IAWN notification will tell about the probability of the impact, impact date, risk corridor, asteroid size, and expected damage estimates. The notification would include points of contact and graphs on the orbit of the asteroid and impact corridor for a 1% probability of impact cases. Some background on why information is being sent and contact details for more information are also provided. More details will be provided later by subject experts.

Based on the IAWN notification, SMPAG will make recommendations, such as the launch of reconnaissance missions, to find more details about the asteroid. The role of the United Nations Office of Outer Space Affairs (UNOOSA) would be to notify the member states.

It is important to note that IAWN signatories also function as a part of their national structures and follow national procedures. As data is public, information travels fast, and information may have been released even before IAWN releases the notification. But IAWN can track and post credible scientific information, which is useful in fast-evolving situations to ensure calm prevails over panic.

The 6-year original Mission of asteroid Ryugu has successfully finished. The JAXA Hayabusa2 spacecraft returned 5.4 grams of material from the surface of a primitive C-type asteroid, 162173 Ryugu, on December 6, 2020. The sample was found to be rich in organic molecules.

The Mission is now extended as Hayabusa 2 SHARP (Small Hazardous Asteroid Reconnaissance Probe) with planetary defense objective to other asteroids. The focus of SHARP is on very small asteroids, of size around 30 metres, whose impact probability is high, making them strategic objects of study for a very realistic planetary defense scenario.

The final rendezvous target for SHARP is in 2031, with the near-earth asteroid 1998 KY26 having a diameter between 20m-40m and a spin period as short as 10.7 minutes. As the spacecraft has only one target marker and one projectile left, collecting samples would not be possible. However, the target marker and the projectile could lead to interesting experiments.

There is also a planned flyby of asteroid (98943) 2001 CC21 in the year 2026. This would be a high-speed flyby at the closest distance of around 100 km. This distance could be risked if the asteroid does not pose a risk to the spacecraft, but very precise navigation would be needed. This asteroid is unique as its centrifugal forces are larger than gravity on the entire surface except in the polar region because of its fast rotation.

Santoshi Tanaka Department of Solar System Sciences at Japan Aerospace Exploration Agency (JAXA): What if Ryugu hits Earth?

Hayabusa2 reached asteroid Ryugu in December 2014. The asteroid's size is around 900 meters. Hayabusa spacecraft determined asteroid Ryugu to be top shaped rubble pile covered with massive rocks. The maximum size of the rubble is not clear.

Hayabusa2 landed several rovers on the asteroid and hit the space rock with two projectiles. The size of the crater created was about 20 metres in diameter.

Ryugu's detailed remote sensing survey and sample analysis have revealed the mechanical properties of the asteroid for the first time. While no information could be gleaned about its mechanical strength, its density was found to be higher than water. The sample collected is still sufficiently voluminous that future measurements are expected.

Interestingly, if the Ryugu asteroid were headed to Earth and entered the planet's atmosphere at an angle of 45 degrees and a speed of 17 kilometres/second, the rubble pile asteroid would break up at an altitude around 40 km above Earth and create an "airburst" similar to the Chelyabinsk meteor over Russia.

Many people will be at the table for a meeting on asteroid impact risk assessment and deflection. The National Preparedness Strategy has a list of agencies, state departments and organizations that would be convening for planning for this disaster.

Planetary defense and NEO hazards are multilateral issues, as their impacts would be felt regionally and globally. Thus the best starting point would be to address these issues as a part of a very wide international cooperation model. 

The success of the NASA DART mission and technology has shown that we should recognize the ingenuity of the worldwide science and engineering community to come up with scientific and creative options to deal with the challenge. So we should remain optimistic about human capabilities to deal with the challenge. 

Halilu Ahmad Shaba, Director General of Nigeria's National Space Research and Development Agency: Contribution of Nigeria

As asteroid deflection is a transboundary issue, the discussions related to deflection would happen at the African Union (AU) as many African countries would be in the path of the risk corridor. Meetings would also occur at sub-regional and national levels. For instance, the Economic Community of West African States (ECOWAS)  has a disaster early warning programme with national space agencies as its stakeholders.

Nigeria has its Nigerian Space Agency, whose space council is headed by the Nigerian president and could bring together major decision-makers and other stakeholders.

However, none of the African countries currently have the capability to deflect the asteroid. Thus collaborations would be needed with other countries for technical expertise and for financing any deflection mission. But African continents need to learn more and develop capabilities for the future.

Legal and Ethical Issues

Jack Beard, Associate Professor of Law, University of Nebraska College of Law: Nuclear Weapons

Nuclear weapons are highly regulated to prevent extensive destruction. Therefore, promoting their use as a humanitarian tool creates an uncomfortable dilemma. Escaping international regulations against their use in a short timeframe would be impossible.

To address this, international cooperation is necessary. The United Nations Security Council could invoke Chapter VII of the United Nations Charter, which deals with actions related to threats to peace, breaches of peace, and acts of aggression.

When it comes to making a decision to act, the initial assumption is that a sovereign state has the freedom to act as it wishes. This is true unless there is a specific prohibition in international law, such as the use of nuclear weapons.

In the case of addressing an incoming asteroid, a country has the ability to decide unilaterally to act against an incoming asteroid. It does not require permission or authorization from an international organization or body.

2029 Apophis Fly-By
Another topic discussed at the conference was the Apophis Fly-By in 2029. This rare occurrence will allow for research opportunities, as it will be so close to Earth that it could possibly change the asteroid's orbit and shape. Space agencies from around the world have already started organizing space missions to reach the asteroid before impact and measure its physical characteristics accurately, which will enable before-and-after impact comparisons to be made.

The OSIRIS-REx mission (the extended mission is now called OSIRIS-APEX), originally intended as a sample return mission targeting the asteroid Bennu, was also discussed. 

A presentation was given by Tomas Kohout on Pre-encounter Mission Requirements to Complement OSIRIS-APEX Post-Encouter Studies of Apophis. He talked about the pre and post encounter goals of the mission.

NASA has decided to extend the mission to visit Apophis, orbiting the asteroid for 15 months and touching down on it, advancing our knowledge of asteroids in the stony class but also providing an opportunity for future analysis of the asteroid Apophis during and after the fly-by. 

Hypothetical Asteroid Impact Simulation
As in every Planetary Defense Conference, there was a hypothetical impact scenario where an asteroid was on a collision course with Earth. Over the first few days of the conference, international decision-makers, including people from the United Nations, the White House, Space Agencies, and Lawyers, came together to discuss the scenario and disaster management measures that could be taken.

The simulation exercise was designed by Paul Chodas alongside Brent Barbee, Lorien Wheeler, and Jessie Dotson. The exercise started with the discovery of an asteroid and its designation as a potentially hazardous asteroid (PHA) with a low impact probability. The impact probability starts to rise and becomes 1% over 3 months. This is the threshold to make some decisions. 

The potential impact is 13 years away, and the date of impact is predicted. But the size of the object is uncertain. And making decisions in the face of uncertainty is what simulation exercise is all about. 

Asteroid size is the biggest uncertainty. It is estimated to be 220 metres - 660 metres. But there is a possibility it could be a dark object, and hence its size could be as large as 2 kilometres. This could mean that we may have to plan for scenarios of nuclear deflection.

The data source is mostly optical from the ground and includes astrometry and photometry data. The asteroid is too close to the sun for the use of JWST to get more information. And it is too far to get data from the radio telescope! This means that no data can be gathered from space.

Its orbit is slightly eccentric, and its orbital period is similar (but slightly shorter) to that of  Earth. Thus over time, the asteroid would catch up to Earth and may collide. Some potential impact points can be calculated with available data, but uncertainty is high. 

I really enjoyed this exercise. It was thrilling, but I also got a good understanding of the importance of my research on developing algorithms to determine the physical properties of asteroids using ground-based data. 

The Role of the United Nations Office for Outer Space Affairs
The conference was an opportunity to understand the role United Nations, especially United Nations Office for Outer Space Affairs, plays in planetary defense. Pursuant to the General Assembly resolution 71/90, paragraph 9 of 6 December 2016, the United Nations Office for Outer Space Affairs serves as the permanent secretariat to Space Mission Planning Advisory Group (SMPAG). 

Questions I Asked the Presenters and Panelists:
At the end of each session, time was set aside for asking questions. I took this opportunity to ask several questions during the conference.

1. Would the ejecta coming out of Dimorphos post-impact fall onto Didymos creating a change in its rotation period?https://media.un.org/en/asset/k1w/k1wmm41pmt?kalturaStartTime=6987&kalturaStartTime=6990

2. If an asteroid were on a collision course with the earth and planned to impact, say, in 30 years, would we try and deflect it right away or wait a decade or so till we had more advanced deflection technology? https://media.un.org/en/asset/k1i/k1i13zivsx?kalturaStartTime=5102

3. Why did the CNEOS size calculator not predict the correct size of Didymos using a correct albedo of 0.15 and Didymos' absolute magnitude? https://media.un.org/en/asset/k1b/k1bffqyw9r?kalturaStartTime=7823

Concluding Note:
Overall, the conference provided a fantastic opportunity for me to learn about the latest developments in asteroid research and share my own research and ideas. The hypothetical impact scenario also provided an opportunity for us to engage in discussions about disaster management measures that could be taken in case of a potential asteroid impact.

Resources

Conference Website and Video Recordings: https://www.unoosa.org/oosa/en/ourwork/topics/neos/2023/IAAPDC/index.html 

Conference Summary Report
https://iaaspace.org/wp-content/uploads/iaa/Scientific%20Activity/conf/pdc2023/pdc2023report.pdf