On 6 March 2006 I published at Astroseti.org a translation into Spanish news about the discovery of Kebira impact crater, a 31-km (19-mile) diameter structure in Egypt, on the border with Libya, by investigators from Boston University.

Two days later I decided to check how this crater appears using the Google Earth program, as I knew image quality can vary from one place to another. I thought that the silhouette would be hard to appreciate, and that would be the reason it took so much time to discover. But, following the article guidelines, I went directly to the Egypt/Libya border, and, in less than a minute, I found the structure (Fig. 1).

Suddenly these questions came to me:

No one saw this before?

How can a 31-km diameter structure not be noticed?

So I decided to explore Google Maps for a while to check for similar structures.

Just past the Libyan border in Chad, "flying" high at 195 km (121 miles), another circular structure appeared on my screen (Fig. 2). A closer look showed, apparently, a typical impact structure, not one of volcanic origin. Of course, finding an impact crater has no merit if it is already known. So I checked by visiting the Canadian Brunswick University impact crater database in Canada. None of the listed craters matched my discovery.

After a while I decided to "take off," but a few seconds later another suspicious structure just 50 km (31 miles) away caught my attention (Fig. 3). I went closer and found that my first impression, again, was that it was another impact structure. Once again it was not in the Brunswick University database.

Finding impact craters could not be so easy! Was I suffering such excitement that I was seeing impact craters everywhere?

I searched the web for more information and found http://www.impact-structures.com/ curated by two geologists, Kord Ernston of Würzsburg University, and Fernando Claudín, a member of the Barcelona Museum of Geology. They were linking to a more comprehensive and updated database. I sent them the images and waited for their comments.

Fernando Claudín's answer was quite fast: "Circularity doesn't mean anything by itself for identifying an impact structure", he said, "but in the first structure the external ring has layers inclined outwards, and the internal ring has a central elevation. It doesn't look volcanic."

About the second crater he wrote, "...not as pronunciated as the first one, but you can appreciate two rings, external and internal, with some paths (and that's good because it means outcrops). The central zone seems collapsed, limited by internal ring."

Confirmation is basically a financial problem : "...it is necessary do some fieldwork with geologists to check if there are breccia, impact metamorfism, etc.

Figure 3. View of the second crater found by the author as seen from an altitude of 5 km (3 miles).

The best for my emotional stability was, without doubt, that he wrote, "It doesn't seem you have the impact discoverer fever. There's enough base to investigate."

So we have two craters (Fig. 4) that look like they were caused by asteroid impacts, but they need a field visit for confirmation.

Figure 4. Both craters are quite close to one another.

There could be a mistake somewhere. Even when I was checking point by point, I could still not believe I was the first one to see those two structures, so I searched for more information on impact craters in Chad. Google showed some results about Aorounga, a crater that obviously was already in the known impacts database, but there was a link explaining how Adriana Ocampo, a JPL geologist, had detected other impact craters close to Aorounga by using radar satellite images. But she also needed to confirm those discoveries. Was it possible that Adriana's impacts and my impacts were part of the same chain of impacts? Once again I opened Google Earth and traveled to the Aorounga area, high enough to have both groups of craters in the same screen. The distance was 300 km (186 miles), but all of them were in line!

I wanted to have more confirmations before publishing these findings, because I didn't want to do something that later could became a fiasco. Fernando Claudín wanted Jord Ernstson to give his own opinion, so I waited (im)patiently until his mail arrived: "Congratulations! The structures you discovered in fact look very promising." Then he continued, "Having two more craters in Aurunga line is fantastic," something similar to the impact chain they are studying in Azuara, Spain, between Teruel and Zaragoza.

The story still continues. Right now I'm still waiting for answers from the Canadians, from David Morrison (curator of NASA's http://impact.arc.nasa.gov/) and Adriana Ocampo, who found this discovery interesting enough to confirm her theory about Aorounga if all craters have the same dates.

But the most important aspect of this report is, probably, that using a free distributed software (Google Earth, and I'm also using NASA World Wind) anyone can search for similar structures. Probably I was very lucky, for, after this success, I spent many hours searching for more structures without results.

Anyway, if you have decided to search for impact structures, avoid confusing them with volcanoes, then check all available known and candidate impact databases and then, and only then, contact a geologist!

Good hunting!