This week's headlines have touted new discoveries purporting to solve two of the Top 10 astronomical mysteries that I wrote about in my book, On the Cosmic Horizon. As I will describe below, the headlines are probably correct concerning a solution to Mystery #9. In a follow-up e-mail to come shortly, I'll explain why the cover of Time magazine (June 25, 2001), overstates the case in claiming that "scientists have just solved the biggest mystery in the cosmos" ---and not only because they're talking about Mystery #3 as opposed to #1!

Let's start with the new headlines relating to Mystery #9, "Where are the Sun's Neutrinos?" Of course, the best way to understand the headlines is to read the Mystery in On the Cosmic Horizon; after all, the reason I wrote the book was to help you understand the astronomy headlines. But for those of you who are stilled filled with anticipation as you wait to find time for reading the whole book, hereีs a synopsis:

In brief, Mystery #9 concerns the fact that theoretical models of how the Sun shines tell us that the Sun should be emitting prodigious numbers of tiny particles called neutrinos --- so many that about 1,000 trillion neutrinos will pass through your body while you read this sentence. Until now, however, special observatories built to detect these neutrinos were finding only about one-third to one-half as many neutrinos as theory predicted. This might have meant that our ideas about how the Sun shines were wrong, but most scientists have hoped there was an alternative explanation with the neutrinos themselves: namely, that some of the Sun's neutrinos could "hide" by changing into other types of neutrinos that made them undetectable by standard detectors. The new headlines are based on first results from the Sudbury Neutrino Observatory (SNO) in Canada, combined with previous results from Japan's "Super-K" neutrino detector, which appear to confirm this explanation. Of course, the results won't be considered definitive until we have several more years of consistent data. But if they hold up, we now have the answer to Mystery #9's question: the Sun's neutrinos were there all along, they were just hiding from our earlier detectors.

Assuming the Mystery is solved, what does it all mean? Here's a brief list of the most significant implications, in order (in my opinion):

1. The fact that observations of solar neutrinos now agree with the theoretical predictions represents extremely strong evidence that we really do understand how the Sun shines. In other words, we can have great confidence that we understand the nuclear reactions taking place deep within the core of the Sun --- and by extension, that we also understand the nuclear processes that occur in other stars.

2. Because the solution confirms that neutrinos can change type, we have further evidence that neutrinos must have mass (for prior evidence, see Mystery #9). This means that the "standard model of physics" cannot be complete as it stands, and therefore that physicists have a lot more work to do before we can truly claim to understand the nature of matter. On the more positive side, the new data also appear to rule out the disconcerting possibility of "sterile" neutrinos (also discussed in the book), which had been raised by previous experiments.

3. The fact that neutrinos have mass also means that they must represent at least some fraction of the mysterious dark matter that dominates the mass of the universe (see Mystery #2). However, the results to date also suggest that the neutrino mass is extremely small, making it highly unlikely that they represent a very significant fraction of the dark matter.

For more background and information on this exciting discovery, I encourage you to read Mystery #9; aside from the "punch line" of the mystery being resolved, it remains accurate. To read more on the discovery itself, go to http://www.sno.phy.queensu.ca/sno/first_results.