Pence, 24, suffered the injury while sliding into second base on Sunday in Pittsburgh. The initial X-rays were negative, but an MRI exam and a second set of X-rays taken on the wrist Monday revealed the more serious injury.
Pence initially expected to be able to play Monday, but realized in the morning that he was dealing with a bigger problem.
"I felt it this morning when I woke up," Pence said. "I was like 'Oh, this isn't healing.' It didn't feel the way I wanted it to. I want to be out there. I love to play. It's very disappointing.
"I'm doing everything I can to get back out there, and hopefully the season's not over for me."
Pence came to Minute Maid Park very sore and swollen Monday, and the Astros were informed of the injury's severity shortly before game time.
"We're very unfortunate to lose a young player who's had such a good impact on this club at this point," Purpura said.
"It's a big blow to the offense," Monday starter Chris Sampson said. "He was the main part of our offense, and losing Hunter is definitely going to hurt."
Pence heads to the disabled list with a .330 average, leading all rookies in extra-base hits (43) and total bases (176). His slugging percentage was the highest of any Astros hitter.
"Hunter was tremendously productive for us, and it's a big blow to our team," potential replacement center fielder Chris Burke said. "We're going to miss him."
Pence has injured his wrists sliding into bases before, but it's usually been his left wrist and he's also been quick to heal.
"I wear a guard on my left wrist because it's usually the one I slide on," Pence said. "I hurt [the left one] earlier in Colorado pretty bad, but I was able to play through it. I thought it was the same thing as that [at first]. But this one, it's not as good as it was before.
"My approach has always been a sideways jump thing. I really don't know what I do or how it happens. I was trying to get a guy that was behind the base, and I have to find a way to do it a little [safer] and do the best I can to disrupt him."
According to Pence, doctors said the ligament was being pulled, and instead of tearing, the ligament pulled off a part of the bone with it.
The injury likely eliminates Pence from winning the National League Rookie of the Year Award. Although Pence was previously considered the favorite, Milwaukee's Ryan Braun has come on very strong of late, and it's very unlikely Pence will have the at-bats when he returns to make up for the time lost.
On the field, it's unclear where the bulk of playing time in center field will go. Manager Phil Garner didn't commit to a specific plan after Monday's loss, saying he would "mix and match" depending on the situation. At home, it seems likely that Burke will receive the bulk of playing time. The Astros considered Burke their everyday center fielder in April, and he's played sporadically there since being recalled in June.
In addition, one of the Astros' goals in the second half of this season is to evaluate where Burke fits in their long-term plans, so they're likely to use the opportunity to give him more at-bats.
"I'll play wherever Phil wants me to play," Burke said. "I've gotten quite a few starts out there, so I feel confident."
On the road, however, the situation becomes murkier. Previously, the Astros had committed to playing Burke at second base and using Craig Biggio off the bench. So, one option is to give Biggio more road starts and use Burke in center.
However, should the organization remain committed to giving Burke playing time at second, there are other possibilities. One is Eric Bruntlett, who started in center field in Pence's place on Monday. Another is Lane, the power-hitting outfielder who struggled to a .165 average while playing the first two months in Houston.
But after being demoted to Round Rock, Lane has turned things around. He hit .308 with eight home runs and 35 RBIs in 42 games, and he gives the Astros the best opportunity to replace Pence's extra-base power. For Lane, it's an opportunity at redemption.
"Obviously, you hate for anyone to get hurt, but I'm excited to get back with the team," Lane said via cell phone on his way to Houston. "I just hope I can contribute, help out. That's what I've been hoping for the whole time [in Round Rock]. You hate for it to be an injury, but I'm glad to be back.
Lane says the opportunity to play every day has helped him to correct problems at the plate.
"I feel great," he said. "It's been fun playing every day. I got into a groove with everyday at-bats. When you get into a groove, it makes the game fun."
Lane will be available for Tuesday night's game.