Scientists at Nasa are celebrating a major success after seeing a probe crash successfully into the heart of a comet.
The washing machine-sized "impactor" collided with Comet Temple 1, releasing a spray of debris from beneath the comet's surface.
Scientists hope the project will help them understand the creation of the Solar System by examining the composition of the comet.
What is your reaction to the Deep Impact comet mission?
This debate is now closed. Read a selection of your comments below.
The following comments reflect the balance of opinion we have received so far:
The Deep Impact mission proves that if you throw enough money at something you are bound to hit it.
I think it is wonderful. As a retired engineer, I just wish I could have been in on it. The math required is mind-boggling.
Mollie Crockett, Barling, AR, USA
Just read that some Russian astrologer believes this will upset her horoscope. However, all her worries will miraculously evaporate if Nasa gives her a few hundred million dollars. Well, at least it gave me my first good laugh today!
Steve, Auckland, NZ
What a waste; I'm absolutely ashamed of being a homosapien who lived to see mankind's stupidity to try and self obliterate by spending millions. I rather see hard earned tax payers money spent on insuring the survival and well being of the majority who dwell on this planet - the poor and the forgotten.
Mike, Washington, DC
This experiment seems it may pay off down the road, but I am agitated that things like this seem to take precedence over more urgent issues like developing alternate energy sources.
Blake, Lansdale, PA, USA
Awesome indeed! That humans can find and hit something so small in so vast a space and to see it happen live even to all on earth. It makes one wonder how much more can man do.
Elton Wong, Singapore
After hearing the news, I told some friends over dinner about Deep Impact's success. No-one believed me; they thought I was making it up. The impact into the comet is almost too hard to believe myself; it is like out of a Hollywood film.
John, Berlin, Germany
As always, there will be those who claim that this is a waste of money, when there are so many problems in the world. Well, you know what? This world will always have problems. At least these people are trying to further mankind's knowledge, and progress us into the future.
If we spend nothing on advancing ourselves until all the world's other problems are solved, we may as well drop our tools, and climb back up into the trees. I say go for it, guys! Keep chucking those fridges, and make our race all the better for it!
WD, Yorkshire, UK
Is this where we find out if Sir Fred Hoyle and Chandra Wickramasinghe were right about their theory of life being carried through space on comets? Are Nasa looking for signs of this?
Trev, Stevenage, Herts, UK
One of the top achievements in space so far. This brings the idea of blasting an object (comet, asteroid, meteor) off collision course with Earth many steps closer.
Rakesh, London, UK
Awesome! The best Independence Day fireworks since 1776! Congrats Nasa, keep on pushing the envelope, there's a whole universe to explore and learn about. Our future is in the stars, just as our past has been.
PM, NYC, US
Your report about the USA's achievement features a comment from a European scientist working on a similar project. Surely the study and exploration of the cosmos would benefit greatly if the expertise and cost were shared between rich countries with space programmes instead of them competing with each other. It seems silly to let the political boundaries we have placed on this planet hinder the progress of such important, fascinating projects.
Fi, Birmingham, England
The methods involved in trajectory calculation and satellite control may benefit us one day when we need to "shoot down" an asteroid heading our way? Well, sounds good, anyway!
Roger Oliver, Le Soler, France
Have Nasa scientists thought of the possible consequences of their 'successful probe'. What if the loss of matter and the explosion itself has changed the orbit? Even one or two degrees could put the comet on a collision course with any part of the universe. This celebration could come back to haunt the earth! Maybe not in our day but in the future.
Kate Knight, Hereford, UK
We are likely to get some good science out of this mission. The motivation for Deep Impact is evolution based. Secular astronomers hope that the data will provide clues on the origin of our Solar System. They believe comets are 'leftovers', and contain relatively unprocessed materials. In reality, the very existence of comets argues against this: comets are continually being disintegrated by solar radiation, they cannot last for billions of years; this forces secular astronomers to make extra assumptions (such as new comets being generated by an unseen Oort cloud) to make the evidence fit. But comets are perfectly consistent with a younger age for the universe.
Kim Kaze, Bristol, UK
I haven't a clue what this will do for science, but there's a real childish pleasure in smashing a washing machine sized lump of metal into a huge snowball at incredible speeds!
As a scientist, it's always good to keep abreast of your own, and other research fields. However, I'm not so sure of the benefits that this expensive line of research will prove/disprove. Does mankind benefit in anyway shape or form by attempts to guess the creation of our Solar System?
Colin Grant, Manchester, UK
Who authorizes this cost. When the world we live in needs help. It is like the blind leading the blind, why are we trying to explain how we were formed, and allowing our world to be destroyed by humans. America stop wasting money and help the poor countries.
What will Deep Impact mission reveal? - Some little green men wondering "who the heck is firing washing machines at our cosmic mobile home, this is war "!
Chris, Horley, Surrey, UK
It is another ant's step to go around the equator on the way of understanding the secret of space!
Tolga, Istanbul, Turkey