“The Asteroid Hunter, A Scientist’s Journey to the Dawn of the Solar System”

Review by Duncan Lunan

Results from the sample-return mission of the OSIRIS-REx spacecraft to the asteroid Bennu in 2023, and before it Japan’s Hayabusa-2 mission to the asteroid Ryugu in 2020, are very much in the news at present – see ‘The Sky Above You, September 2025’, ON, 2^nd September.  Dr. Dante S. Lauretta became Principal Investigator of the OSIRIS-REx Asteroid Sample Return Mission in 2011, as well as a co-investigator on the Hyabusa 2 mission, and now on ESA’s HERA mission, the follow-up to the DART asteroid impact, now in flight.  His book tells the story on several levels, interspersed with short chapters following the history of the asteroid since the beginning of the Solar System, not of course covering the most recent discoveries, but focussing on the possibility that Bennu might collide with the Earth on September 21^st 2182, if no steps are taken to prevent it.  (It must be said, because he doesn’t, that the chance of impact is currently put at 1: 2700, with a slightly higher chance of 1: 1750 over the next 300 years.)

His own interest in space science began with the Search for Extraterrestrial Intelligence, eventually concentrating on the origins of the Solar System, and therefore possibly others.  At the University of Arizona, he gravitated to the study of Mars and became part of the Mars Observer project, NASA’s first mission to Mars since the Viking landers of the mid-1960s. 

He joined a month before the very advanced probe was due to arrive  (Fig. 2), only for it to be destroyed by a fuel explosion as the engine was being pressurised for retrofire, as I mentioned in ‘Little Red Dots, Interstellar Comet’, ON, 24^th August 2025.  

In the vacuum created by that event, NASA turned to looking for signs of life in meteorites from Mars, and Lauretta took the opportunity to join a six-week search for meteorites exposed on the snowfields of Antarctica, working out of the big US base at McMurdo Sound  (Figs. 3-5.  As the book is sparsely illustrated with just a few black-and-white images, I’m making my own selection to illustrate these points.) 

Most Martian meteorites are shergottites, water-bearing rocks whose isotopic ratios show clearly that they’ve come from Mars;  most are found in the deserts of North Africa, but ALH84001, the one that showed possible signs of life, came from the Allan Hills in Antarctica  (see Fig. 3).  The US team were searching mainly for stony shergottites and carbon-bearing chondrites, but Lauretta also introduced the use of metal detectors to find nickel-iron meteorites, core fragments from asteroids large enough to be heated by radioactive decay and differentiated.  NASA’s Psyche probe is on the way to a particularly large one now.  As it happens, I’ve also just read John Knight’s The Crossing, Sir Vivian Fuchs, Sir Edmund Hillary and the Trans-Antarctic Expedition 1953-58  (Amberley Publishing, 2018, Fig. 6), and it’s fascinating to see how things have moved on in the meantime – and where they haven’t.  

One lesson that Lauretta learned was that even in Antarctica, meteorites are rapidly invaded by terrestrial bacteria, and the naturally formed organic compounds in the chondritic ones are contaminated and consumed.  The need to find pure examples was a major driver of what became the OSIRIS-REx mission.  The name grew naturally out of a list of objectives that Lauretta drew up when invited to join the project, ‘REx’ was added for ‘Regolith Explorer’, and they made ‘Bennu’, the mythological Egyptian bird, a natural winner of the schools competition to name the asteroid.

Initial NASA approval was awarded in 2006, after several false starts, and the classification of Bennu as ‘potentially hazardous’ bumped up its priority.  In 2011, as the project gained full NASA approval, the resignation of the previous Principal Investigator put Lauretta into the hot seat, although he lacked the usual management and negotiating experience to head the rapidly growing but disparate team of experts involved.  A great deal of practical experience came from Japan’s Hyabusa mission to asteroid Itokawa, a sample mission which returned only a few grains of material, valuable as they were;  from the failure of Mars Polar Lander, and the success of its Phoenix successor;  the actual disaster of Mars Climate Observer due to a mix-up of Imperial and decimal units;  and ESA’s Rosetta mission to Comet 67-P, which succeeded in all respects except for the crash-landing of the Philae lander.  All the way along, the major uncertainties lay in the composition of the Bennu surface, and just how to acquire material from it.  Tests of a prototype in microgravity on NASA’s ‘Vomit Comet’ parabolic aircraft were encouraging, but huge uncertainties remained.  These were reflected in challenges to the viability of the mission which went beyond the scientific and technical issues into the internal politics of NASA, including wrangles between different research centres and competing proposals.  All of this is spelled out in the book, in far more detail than I can summarise here.

The launch of OSIRIS-REx on an Atlas V booster went flawlessly on September 8^th, 2016  (Fig. 7), as did the Earth flyby of 22^nd September 2017  (Figs. 8 & 9).  On arrival later that year, Bennu’s surface proved to be a lot more inhospitable than expected, completely covered with boulders which we now know to have come from all over the Solar System, and from interstellar space  (Figs. 10-11), with the further complication of some being ejected as asteroid and probe approached the Sun  (Fig. 12). 

The original timescale for selection, rehearsal and sampling  (Fig. 13)  had to be repeatedly extended, and when an impasse was reached with 16 possible landing sites, a timely intervention from an independent study by Brian May was crucial in narrowing the choice to four  (Fig. 14). 

 The final sample capture wasn’t achieved until 20^th October 2020  (Figs. 15-17).

After the difficulty with which Hyabusa and Hyabusa 2 collected just a few grains of dust, the OSIRIS-REx aim to collect two ounces was considered ambitious, even after close rehearsal passes over the site. But in Bennu’s microgravity the puff of gas with which the spacecraft arrested its descent stirred up ‘a blizzard of rocks’, momentarily blinding the camera, hurling debris for 60 metres and filling the sample container to overflowing, so that it couldn’t be closed until surplus material had leaked out. Having packed it up, OSIRIS-REx achieved final surveys of the site, and departed for Earth (Fig. 18).

The return to Earth in September 2023 was another cliffhanger  (Fig. 19), with the drogue parachute failing to open after re-entry in what briefly looked like a replay of the Genesis solar probe’s return, when the chutes failed altogether, the capsule burst open on landing and the priceless solar wind samples, embedded in aerogel, were exposed to atmospheric contamination.  When that happened in 2004, Prof. Colin Pillinger said he had been waiting for them since the Apollo landings ended in 1972, and the loss of them was a bigger disappointment than the failure  (near-success, as it turned out)  of the Beagle 2 Mars lander the same year.  But the OSIRIS capsule’s main chute opened and it landed successfully in Utah  (Fig. 20), after which the sample container was taken to the Lunar & Planetary Receiving Laboratory at Johnson Space Centre in Houston  (Fig. 21).

That’s where the hardback book leaves it, though I notice online that the paperback has ‘an added exciting chapter’. 

There was indeed a further cliffhanger to come, because when the container was opened there was Bennu dust inside  (Fig. 22), and the lid of the uncontaminated sample canister remained stuck fast for three months before it was finally breached  (Figs. 23 & 24) once a special tool had been made to do so in sterile conditions. 

To repeat what I said in ‘The Sky Above You’, “continuing study of the samples has confirmed that its crust contains material from interstellar space pre-dating the origin of the Solar System, and materials formed at different distances from the early Sun, which continue to tell us more about it and about the dust and gas from which it and the planets formed.  In particular, the water bound up in the different types of rock may resolve the question about where the Earth’s water came from – within the planet, or by bombardment? – and the naturally formed organic compounds will tell us more about the precursors to life here.  (Elizabeth Howell, ”Potentially hazardous” asteroid Bennu contains dust older than the solar system itself — and traces of interstellar space’, MSN News, online, 26^th August 2025.)  It appears that the parent body which formed from these materials, and then shattered in subsequent collisions, formed in the same part of the early Solar System.  They may even have had the same parent body, of which the Polana asteroid group in the Main Belt are the surviving fragments, with Polana itself much the largest at 55 km across.  Both Bennu and Ryugu have been pushed nearer the Sun by Jupiter, and their surfaces have evolved differently in consequence.  (Evan Gough, ‘It’s Official:  Asteroids Ryugu and Bennu Are Siblings’, Universe Today, online, 19^th August 2025.)”

And as we go to press, there’s more major news.  Ongoing study of the dust grains brought back by Hyabusa 2  (Fig. 25)  has found that water-soluble, radioactive elements have migrated towards the crust of Ryugu  (and by implication, also in Bennu, if they had the same parent body)  over a period of a billion years, long after Ryugu separated from Polana  (Fig. 26). 

It means there must have been much more water in the early chondritic asteroids than was thought, and makes it much more likely that Earth’s present oceans came in the early bombardment.  (Robert Lea, ‘Scientists find evidence of flowing water on Ryugu’s ancient parent asteroid. “It was a genuine surprise!”‘, Space.com, online, 10^th September 2025.)

Meanwhile, we still have the prospect of a collision with Bennu in 2182  (Fig. 27).  It was hoped that we might learn a lot more about that issue generally from the extended OSIRIS-APEX mission to orbit asteroid Apophis after its close flyby in 2029, but barring any sudden change of heart by the present US administration, instead it is to be turned off in a few weeks from now, despite being fully operational.  To quote Kurt Vonnegut, “so it goes”.

Duncan Lunan’s recent books are available from bookshops and through Amazon;  details are on Duncan’s website, www.duncanlunan.com.