"Everything up to now, all these missions, they've been preparations, fine-tuning for this moment. Not that the other work wasn't important or didn't matter, but if we successfully deflect asteroid Helios 685, we alter the course of humanity so profoundly it's highly probable that the time we come from, everything between then and now, the plagues, the shortages, the wars, none of that will happen."
Grant MacLaren[src]

Helios-685 is an asteroid that would have collided with Earth in the year 2018 were it not for the intervention of the Travelers. Helios would have been detected sixteen months prior to impact, which would be too late to prevent it. The asteroid would have struck the Atlantic ocean, causing a tidal wave that swept over the Eastern Seaboard. Philip Pearson claimed the death toll from the original impact was 91,462,000. The resulting resource shortages caused widespread famine and warfare.

Traveler teams across the world worked for over a year to prevent the impact, which was initially believed to be the source of all humanity's ills in the future. An initial version of the Grand Plan involved assembling an antimatter laser to deflect the asteroid by 0.07 degrees - enough to barely miss the Earth. The Director reasoned that the near-miss would give humanity an opportunity to reflect on how much they had to lose.

The laser struck the asteroid and deflected it successfully eighteen months before the historical impact date. However, Travelers who arrived in the past after the Helios impact was prevented reported no changes in the future; Aaron Donner speculated that the future had actually gotten worse. This was later revealed to be at least in part due to the survival of Doctors Samantha Burns and Amanda Myers and the invention of the singularity engine.

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