If all goes as planned, the event may generate some cosmic fireworks that will help astronomers to better understand comets.
Comets are balls of ice and dirt which orbit the sun in elliptical paths. As they near the sun, solar radiation vaporizes the icy material, which is blasted off the surface forming a cloud of debris called a "coma." Some of the debris is swept away by solar wind forming a luminous "tail" which can extend many millions of miles into space.
NASA's "Deep Impact" spacecraft is designed to study the composition of a comet through an innovative approach: the spacecraft carries a small 370 kg (816 lb) probe which is released from the main spacecraft roughly 24 hours before it reaches Comet Tempel 1. The self-navigating probe is designed to crash into the comet's nucleus (the central solid mass of a comet). In addition to creating a stadium-sized crater, the impact should eject sub-surface icy material into space.1
The larger spacecraft will pass by the comet and will transmit images of the collision from a safe distance. The flyby craft is also equipped with a spectrometer-a device that can determine the composition of ejected material by analyzing the emitted light. The spacecraft will transmit images and spectral data back to earth for further study. If successful, this mission will help astronomers to better understand the internal composition and structure of comets.
What can we expect to see?
The impact is expected to substantially brighten Comet Tempel 1 for a few days due to the reflection of sunlight off the scattered debris. The comet is currently quite faint and can only be seen with a telescope. However, the impact debris may substantially brighten the comet, making it easier to spot with a small telescope under dark skies.
This temporary brightening may last a few hours or several days; however, no one is certain since nothing like this has been done before. Those in the western United States and Mexico will be able to watch the impact as it happens at night (at roughly 10:52 pm on the evening of July 3, Pacific Time). Everyone else around the world will begin seeing the aftermath (i.e., the debris) during the darkness of the July 4th evening.
The worldview connection
As with so many astronomy programs these days, the motivation for the "Deep Impact" mission is evolution based. Secular astronomers hope that the data will provide clues on the origin of our solar system. They believe that comets are leftovers from the formation of the solar system, and so contain relatively unprocessed primordial materials.
In reality, the very existence of comets argues against the secular formation of the solar system: since 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.2 These extra assumptions themselves are problematic.3 But comets are perfectly consistent with biblical creation and a young age for the universe.
Despite the anti-biblical motivations of the "Deep Impact" project, we are likely to get some good science out of this mission. Science itself is biblically based; God has given us an amazing universe and has planted within us the desire to understand it. We are not to be like a mule or a horse "which have no understanding" (Psalm 32:9). Indeed, a study of the universe can give us a greater appreciation of the power and ingenuity of the Lord.
Comets are one element of God's universe; they are part of the lights in the heavens made on Day 4.4 Learning more about their composition can provide a greater appreciation of God's wisdom.
These are the kinds of topics that will be covered in the planetarium at AiG's future Creation Museum in Northern Kentucky, USA. Visitors will learn how the astronomical evidence confirms what the Bible teaches, and how such evidence challenges secular scenarios.
From the most distant galaxies to the subsurface of a comet, all creation testifies to God's invisible attributes (Romans 1:20).