By the end of 2020 or early 2021, Gov. Charlie Baker will have appointed the entirety of the state's top court, including its chief justice, during his first six years in office.

The death of Chief Justice Ralph Gants at age 65 this week and Associate Justice Barbar Lenk's impending retirement in December leave Baker with two vacancies to fill.

"Unlike the United States Supreme Court, where judges sit forever, not so in Mass. with our 70 year constitutional rule that they have to retire at 70. So governors are able, especially if they run two terms, are able to appoint more to the Supreme Court," Governor's Councillor Robert Jubinville told GBH News.

The Governor's Council, an eight member panel elected independently of the governor, will review nomination made by Baker to fill the slots. The Council typically holds lengthy interview hearings with potential SJC justices before voting on whether they should join the court.

Neither the Judicial Nominating Commission, the arm of Baker's office that recommends legal appointments, or Baker's office responded to requests for comment on the vacancies.

Baker appointed five of the six associate justices in his first term: Frank Gaziano, David Lowy and Kimberly Budd in 2016 and Elspeth Cypher and Scott Kafker in 2017. Baker has not yet had the chance to sit a chief justice, since Gants was elevated to the top spot late in Gov. Deval Patrick's second term in 2014.

"He can pick somebody that's on the court and move him up to the chief's position and then appoint somebody for that position," said Jubinville, who has sat on the Governor's Council since 2013.

Jubinville said Baker isn't restricted by the state constitution to picking a sitting judge, or even an attorney, for either of the positions.

"But governors haven't done that in many, many years," Jubineville said.

Baker said Tuesday he'll "need a few days to figure that out," when it comes to the new vacancy created by Gants' death.

"We were anticipating that Justice Lenk was going to retire at the end of October and had just run a pretty comprehensive process, actually reopened it, to collect candidates who might be interested in her seat," Baker said at a press conference Tuesday in Fitchburg.

"Honestly, given the short timeframe between hearing the news about - I mean it's not even 24 hours on Justice Gants - we haven't thought much yet about next steps," Baker said.