The ship that goes to destroy the comet is called The Messiah. This is not only an appropriate name, but also an inside joke. When the first space shuttle was being conceived, NASA constructed a full-scale, wooden mock up of the STS Orbiter. It was nicknamed 'The Messiah' because, according to Flight Controller Jerry Greene, everyone who walked into it said, "Jesus Christ!" in reference to its size.
After discovering the comet, one of the astronomers is killed in a car accident. This mirrors the real life car accident death (July 18 1997, in outback Australia) of astronomer Eugene Shoemaker, who helped discover the Shoemaker-Levy 9 Comet.
One of the NASA officials in the movie is played by Gerry Griffin, who is a former NASA flight director. Griffin presided over the Apollo 12 mission and later became director of the Johnson Space Center in Houston.
The movie begins in the year 1998, where Leo and Sarah's astronomy club is on top of the hills looking at stars and where Dr. Wolf died in a car crash. A year passes, and it's 1999, the year when President Tom Beck announces to the world that a comet would threaten to hit the Earth in one year on August 16. Therefore, the date of the Wolf-Beiderman impact is predicted to occur on 16 August 2000.
During the school assembly, one student makes the observation "You're going to have more sex than anyone else in our class!" to Leo Biederman. This line was improvised by Jason Dohring, and the reactions from the other students are genuine.
The traffic jam scene was filmed on Virginia State Route 234, a bypass that was under construction at the time. The roughly 1,800 vehicles used in the scene came mostly from volunteers from the Washington D.C. suburb of Manassas, Virginia.
An actual giant object from space did once strike the general area of the Eastern Seaboard where "Biederman" impacted in the film. Hitting the Norfolk, Virginia vicinity about 35 million years ago, it created the huge, now-buried Chesapeake Bay impact crater.
The film portrays the wave that struck New York City crashing over and around the towers of the World Trade Center, which were the only buildings barely above water at the end of the sequence, surviving the wave. After the events of the September 11 terrorist attacks, some television broadcasts of the film were edited to remove the buildings.
Director of Photography Dietrich Lohmann was very ill during the production phase of the film, and the cast and crew found out he was dying from leukemia. A special dedication to Lohmann was put in the movie's closing credits, as he passed away not long after the film was finished.
When Marcus Wolf (Charles Martin Smith) is trying to send email about the approaching comet, we see the first few entries in his e-mail inbox. Two of the messages are from "cshoemaker arizona.unv", one of which has the subject line "101 Mir jokes". Carolyn Shoemaker and Eugene Shoemaker are well-known comet experts, credited as "comet advisors" to the movie.
A line was edited in the President's press conference scene. President Beck stated "Life will go on, we will prevail." Originally, President Beck said "Life will go on, we will prevail...THIS IS NOT ARMAGEDDON!" The producers later realized that the movie was going to be in box office competition with the movie Armageddon (1998).
'Deep Impact' was a NASA space probe designed to study the composition of the interior of the comet Tempel 1. On July 4, 2005, one section of the Deep Impact probe successfully impacted the comet's nucleus. This is coincidental, as the scientists behind the mission and the creators of the movie devised the name independently of each other, at around the same time.
Morgan Freeman wanted his character (the President) to be wearing an earring. Director Mimi Leder turned him down. Later we see the President addressing the nation from the oval office. His sleeves are rolled up and one of Freeman's tattoos is showing. The director liked this. She felt it gave the President an everyman look.
In the film's final trailer, the blue background used behind the text graphics is a slightly altered version of the background used for the opening titles of Event Horizon (1997), another Paramount film.
The story revolves around Leo (Elijah Wood), Spurgeon (Robert Duvall), and Jenny (Téa Leoni). Jenny has two scenes with the President, but Leo doesn't have a scene with either of them. In the script Leo was supposed to have a scene in the White House watching the launch of Atlantis with the President.
Of the screenplay, one executive attached to the film said that John Wells "would take three pages and turn them into one, and it was a more compelling page". However, due to his work running the TV series ER (1994), Wells was only able to help out for a few weeks before leaving the project.
The trivia item below may give away important plot points.
When Jenny Lerner is looking up "ELE" on the Internet, the ad banners on the right-hand side of the screen foreshadow the tidal wave at the end of the film: "The Wave of the Future", "You've got some ocean coming", etc.