The greatest scientific breakthrough of 2014 could be a new advance toward curing hepatitis C, landing on a comet for the first time, or three other advances made in the last year.

Science has been one of the most prestigious journals in the world for over a century, and their nominations for the greatest advance of 2014 have been narrowed down to five finalists. Medical advances cover three of the finalists in the contest, along with a discovery in genetics and landing on Comet 67P/Churyumov-Gerasimenko.

In one of the five advances of 2014 being considered for Breakthrough of the Year is the discovery that blood from young mice can revitalize the muscles and brains of older animals. This could hold promise that a similar technique could be used to treat human patients with diseases and disorders related to aging. Medical researchers are already studying the use of blood plasma from young donors to treat Alzheimer's disease.

Type 1 diabetes could soon be treated using stem cells capable of producing insulin.

"The recipe is complex, and the cells-made from embryonic stem cells or reprogrammed adult cells - would still face rejection by diabetics' immune system if transplanted into patients. But the achievement brings a possible stem cell-based treatment for diabetes a step closer," Science publishers stated on the contest Web page.

Hepatitis C may soon be cured using a pair of new treatments that directly fight the virus have reached the market. Previous treatment for the disease involved weekly injections of interferon and almost a year of taking oral doses of ribavirin. New treatment methods could completely cure patients of the disease, although costs could reach $1000 for each dose of the medicine.

For the first time in history, biologists have created new "letters" in the genetic code.

"Researchers have expanded the DNA repertoire beyond the G-C and A-T pairs found in nature by creating a pair of novel letters, X bound to Y. This year they managed to insert these extra letters into living bacteria," Science editors stated in a profile on the discovery. Researchers will next attempt to use the new genetic code to create new amino acids.

The Philae lander touched down on the surface of a comet for the first time, although the landing did not go as planned. The vehicle bounced off the surface of the icy body twice before coming to rest, upright, but in hibernation mode. The spacecraft could come back to life in 2015, as the comet approaches the Sun.

The general public is being asked to participate in voting for the most significant advance in science to be announced during the last 12 months. Votes may be registered on the Web site for the journal Science through December 9.